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EXTRACT  FROM  THE 
UNITED  STATES  ARMY 

X^RAY  MANUAL 

AUTHORIZED  BY  THE  SURGEON'GENERAL  OF  THE  ARMY 

Prepared  under  the  Direction  of  the 
Division  of  Roentgenology 


[219  illustrations} 


NEW  YORK 

PAUL  B.  HOEBER 

67-69  EAST  59TH  STREET 
I918 


Copyright,  191 8 
By  PAUL  B.  HOEBER 


Vuhlished,  October,  191 8 


Vrinted  in  the  United  States  of  America 


TABLE    OF   CONTENTS 


X-RAY  PHYSICS 

X-RAYS  AND  Electricity 

Introduction,  15 
X-rays,  15 
Paths,  17 
Velocity,  17 
Energy,  17 
Scattering,  17 
Passage  through  matter,  18 
Electrons,  18 
Production  of  x-rays,  19 
General    instructions   and   pre- 
cautions, 20 
Electrical  terms,  22 

Charges,  22 

Generators,   22 

Voltage,  28 

The  volt,  23 

Current,  23 

The  ampere,  23 

Eesistance,  23 

The  ohm,  24 

Power,  24 

The  watt,  24 

Derived  units,  24 
Measuring  instruments,  25 
Electric  circuit,  25 
Direct  current  (d.c),  26 
Alternating  current    (a.c),   27 
X-ray    current-voltage    require- 
ments, 27 
High  voltage,  27 

Tubes  and  X-ray  Production 

The  gas  tube,  29 
The  Coolidge  tube,  31 
No  inverse,  35 
Penetration  limits,  35 
No   fluorescence    in    the    glass, 
35 


New  form  of  Coolidge  tube,  36 
Tube  focus,  38 
Conditions  for  operation,  39 
Gas  tube  characteristics,  41 
Danger  in  testing,  42 
Coolidge    tube    characteristics, 

42 
Outflow  of  radiation,  43 
Amount  of  radiation,  44 
Quality,  44 
Dependence     of     quantity     on 

electrical  conditions,  45 
Penetration,  46 

X-RAY  Machines 

X-ray  transformer,  47 
Control  of  the  trausformer,  48 
Eheostat,  49 
Autotransformer,  52 
Inductance  taps,  56 
Transformer  chart,  57 
How  to  use  the  chart,  58 
Synchronous  motors,  60 

Starting,  60 
Polarity    indicator,    60 
Rotary  converter,  62 
Rectifier,  64 
Sparking  troubles,  66 
Noise,  66 
Inverse,  66 

Electromagnet  and  solenoid,  67 
Choke  coil,  68 
Protection  against  surge,  68 
Remote  control  switch,  69 
Line   wiring,    70 
High  tension  wiring,  72 

Care  of  Apparatus 

Tracing  circuits,  75 

Locating  trouble,  78 
Primary  circuit,  80 
Secondary  circuit,  81 


ui 


IV 


TABLE  OF  CONTENTS 


Care  of  tubes,  82 
Care  of  motors,  84 
Care  of  transformers,  85 
Care  of  batteries,  86 
Emergency  provisions,  89 
Polarity  indicator,  89 
Milliammeter,  90 
Timer,  90 
Remote  control,  91 
Protective   resistance,  91 
Motor  or  rectifier,  91 
Autotransformer  or  rheostat, 

92 
Fuses,  93 
Ordering  supplies  and  repairs, 
94 

Induction  Coils 

Coil  characteristics,  95 
Valve  tubes,  96 
Interrupters,  98 
The  Wehnelt  interrupter,  99 

Operating  notes,  99 
The   mercury   interrupter,    100 

Operating  notes,  101 
Tubes  for  use  with  coils,  102 
Readings,  104 
Portable  coils,  104 

Photographic  and  Dark  Room 
Work 

Fast  work,  104 

Photographic  density  and  char- 
acter of  negative,  105 

Exposure  table,  108 

Plates  and  films,  110 

Filling  envelopes  and  cassettes, 
111 

Intensifying  screens,  112 

Care  in  handling  plates,  113 

Tank  development,  116 

Temperature,  116 

Concentration,  116 

Plate  defects,  116 

Examining  negatives,  117 

Developer  action,  117 

*'Hypo"  or  fixing,  119 

Fog,  119 

Developing  formulae,  120 
Hydroehinone,  120 


Elon-hydrochinone,  120 
Edinol-hydrochinone,    121 
Metabisulphite-hydrochinone, 
121 

Fixing  bath  formulae,  122 

Chrome  alum  fixing  bath,  122 

Notes  on  fixing,  122 

Reducing  dense  negatives,  123 

Darkroom,  123 
Arrangement,  124 
Ventilation,  125 
Humidity,  127 

Care  of  utensils,  127 

Supplies,  127 

Marking  negatives,  127 

The  x-ray  negative,  128 

Records,  132 

LABORATORY 
EXPERIMENTS 

Laboratory  instruction  in  prep- 
aration for  Roentgenoiogv, 
133 
Instruction  unit,  134 
Test  plates,   136 
Distance-time    relation,    test 

plate  No.  1,  138 
Distance-time    relation,    test 

plate  No.  2,  139 
Voltage-time     relation,     test 

plate  No.  3,  140 
Summary    of    the    preceding 
relations,  test  plate  No. 
4,  141 
Change  in  time  of  exposure 
with        thickness,        test 
plates  Nos.  5  and  6,  144 
The     Benoist     penetrometer, 
test  plate  No.  7,  146 

NEW  APPARATUS 

Army  x-ray  table,  150 

Setting  up  table  (portable), 

158 
Cautions,  159 

Some  operating  points,  160 
List  of  numbers  referring  to 

illustrations    of     standard 

tables,  162 


TABLE  OF  CONTENTS 


Fluoroscopic  room  illumina- 
tion, 163 

To  find  target-screen  dis- 
tance, 163 

Examples,  164 

Centering  tube  in  the  box  be- 
neath the  table,  165 

The    U.    S.    Army    portable 
x-ray  unit,  167 
Engine,  169 

The  transformer  unit,  171 
Eed    light    for    fluoroscopic 

room,  177 
Limitations,  177 

The  U.  S.  Army  bedside  x-ray 

UNIT,  179 

Limitation   of  tube   current, 

179 
Service  conditions,  180 


Operation,   180 

X-ray  transformer,  183 

Tube,    184 

To  adjust  the  tube,  184 

Care  in  moving,  185 

Exposure,  185 

Accessory  apparatus,  186 

Fluoroscopic  unit,  187 

STANDARD  POSITIONS 

Standard  positions,  188 

DANGERS  AND  PROTECTION 

Dangers  from  the  x-ray,  194 
Protection     of     the     operator 

from  the  x-rays,  195 
Electrical  dangers,  198 
Type  of  control,  199 
Eesuscitation      from      electric 

shock  or  asphyxiation,  200 


LIST  OF  ILLUSTRATIONS 

riG.  PAGE 

22 
25 
26 
29 
33 
33 
34 
36 


1.  Generator  on  open  circuit  ...... 

2.  Simple  electric   circuit  ...... 

3.  Current-time  curve  of  a  simple  a.-c.  circuit 

4.  Regular  gas  containing  tube       ..... 

5.  Coolidge  cathode  construction     ..... 

6.  Coolidge  tube       .         .         .         .         .         .         . 

7.  Wiring  diagram  for  Coolidge  filament  transformer  . 

8.  Eadiator  type  of  Coolidge  tube         .... 

9.  Current    and    voltage    curve    for    self -rectifying    Coolidge 

tube  ......... 

10.  Variation  of  size  of  shadows  of  small  objects  with  a  wide 

focus   tube        ........ 

11.  Current-voltage  lines  of  Coolidge  tube  for  fixed  filament 

temperatures    ........ 

12.  Relation  between  kilovolts  and  spark  gap  . 

13.  Protection  from  surge  by  use  of  a  lamp     . 

14.  Consumption  of  voltage  by  primary  of  x-ray  transformer 

and   series  resistance        ...... 

15.  Rheostat  construction  and  connections 

16.  Theoretical  chart  line  ...... 

17.  Wiring  diagram  of  autotransformer  .... 

18.  Relation  of  x-ray  production  on  rheostat  and  autotrans 

former    control         ....... 

19.  Partial   '' chart '^  of  a  particular  machine  with  rheostat 

control      ......... 

20.  Partial  ' '  chart ' '  of  the  same  transformer  using  autotrans 

former   control  ....... 

21.  Wiring  of  "polarity"  switch     ..... 

22.  Principle  of  polarity  indicator     ..... 

23.  Principle  of  rotary  converter       ..... 

24.  Relation  between  d.-c.  voltage  supplied  and  a.-c.  voltage 

delivered  ........ 

25.  Secondary  circuit  for  four  arm  rectifier 

26.  Secondary  circuit  for  two  arm  rectifier 

27.  Secondary  circuit  for  disc  type  of  rectifier 

28.  Relation   between    an   electric    current   and    its   resulting 

magnetic   field  ....... 

29.  Arrangement    for    constant    resistance    between    filament 

transformer  and  Coolidge  filament 

30.  The   path   of   negative    charge   from    line   through    spark 

gap,  tube  and  milliammeter 

vi 


37 
39 

43 

46 

48 

50 
51 
53 
54 

56 

58 

59 
60 
61 
62 

63 
65 
65 
66 

67 

73 

74 


LIST  OF  ILLUSTRATIONS  vii 

FJG.  PAGE 

31.  Simple  primary  circuit,  rheostat  control     ....  76 

32.  Addition   of   reversing   switch    (polarity   changer)      .         .  76 

33.  Magnetic   control-switch   added   ......  76 

34.  Time       switch      added         .......  76 

35.  Multiple  primary  taps  added       ......  77 

36.  Autotransformer  instead  of  multiple  primary  taps     .         .  77 

37.  Fundamental  diagram  of  x-ray  machines  ....  79 

38.  Use  of  a  lamp  in  trouble  hunting       .....  80 

39.  Softening    and    raising    connections    on    Snook    hydrogen 

tube 82 

40.  Storage    battery   charging    .......  88 

41.  Emergency  rheostat  for  control  of  primary  of  x-ray  trans- 

former      ..........  93 

42.  Emergency  use  of  10  ampere  fuse  wire      ....  94 

43.  Valve   tube 96 

44.  Vacuum  tube   oscilloscope   .......  97 

45.  Operation  of  induction  coil  with  mercury  interrupter         .  97 

46.  Operation  of  induction  coil  with  electrolytic  interrupter    .  98 

47.  Centrifugal  jet  mercury  interrupter  .....  99 

48.  ''Eotax"    interrupter 100 

49.  Oscillogram — induction   coil   current  with  a   gas   mercury 

interrupter        .........  103 

50.  Oscillograms — induction    coil    currents    with    Wehnelt    in- 

terrupter          .........  103 

51.  The  relation   between  exposure   and   density   of  a   photo- 

graphic plate 106 

52.  Finding  speed  factor  of  intensifying  screen       .         .         .  114 

53.  Viewing  box         .........  118 

54.  Simple  arrangement  of  light  for  developing       .         .         .  124 

55.  A  convenient  darkroom  arrangement  .....  125 

56.  Wooden    developing    tank    .......  126 

57.  Simple  ventilator  for  darkroom  ......  126 

58.  Record  and  report  form  for  x-ray  examination  .         .         .  131 

59.  Diagram  of  connections  of  instruction  unit       .         .         .  135 

60.  Machine  used  for  instruction  purposes       ....  136 

61.  Effect  of  scattering  on  undercutting  of  image  .         .         .  145 

62.  Standard  U.  S.  Army  x-ray  table  (Base  Hospital  type)   .  150 

63.  Standard  U.  S.  Army  x-ray  table   (Portable  unit  type)    .  151 

64.  Framework  of  standard  army  x-ray  table  and  operating 

pull   switch       .........  152 

65.  Details  of  tube  box,  cradle  and  shutter         .         .         .  153 

66.  Mounting  of  standard  type  tube  in  army  x-ray  table         .  154 

67.  Tube  box  and  mount  for  radiator  type  tube       .         .         .  155 

68.  Screen-carrying    mechanism          ......  156 

69.  Method  of  handling  screen  and  shutter       ....  161 

70.  Measurement  target-screen  distance,  standard  screen  car- 

rier           ..........  164 

71.  ^Method  of  centering  tube  in  box         .....  166 

72.  United  States  Army  portable  x-ray  unit  complete      .         .  167 


viii  LIST  OF  ILLUSTRATIONS 

FIG.  PAGE 

73.  Wiring  diagram  for  United  States  Army  portable  x-ray 

unit 168 

74.  Instrument  box  for  portable  unit,  front  view     .         .         .  172 

75.  Instrument    box   for    portable   unit   showing   instruments, 

high  tension  terminals,  and  openings  for  connections     .  174 

76.  Connections  for  red  lamp  over  the  fluoroscopic  table,  when 

used  with  portable  or  bedside  unit 177 

77.  United  States  Army  bedside  unit        .....  178 

78.  Position  of  parts  when  using  the  bedside  unit  for  chest 

examination  at  the  bedside     ......  180 

79.  Eotary  converter  used  for  d.-c.  operation  of  the  bedside 

unit 181 

80.  Wiring  diagram  of  connections,  United  States  Army  bed- 

side unit  for  110-220  volt  d.c.  or  110  volt  a.c.       .         .  182 

81.  Wiring  diagram  of  connections  United  States  Army  bed- 

side unit  for  220  volts  a.c.      ......  183 

82.  Position  for  (a)  clavicle  (b)   shoulder  joint       .         .         .  188 

83.  Position  for  elbow,  lateral  view  ......  189 

84.  Position  for  elbow,  anteroposterior  view     .         »         .         .  189 

85.  Position  for  Avrist,  anteroposterior  view     .         .         o         .  189 

86.  Position  lor  wrist,  lateral  view  ...,„.  189 

87.  Position  for  hip  joint,  anteroposterior  view        .         „         .  190 

88.  Position  for  knee,  anteroposterior  view       ....  191 

89.  Position  for  knee,  lateral  view  .         .         .         „         „         ,191 

90.  Position  for  ankle,  anteroposterior  view     .         .         »         .191 

91.  Position  for  ankle,  lateral  view  .         .         .         .         .         ,191 

92.  Position  for  foot,  anteroposterior  view       ....  192 

93.  Position  for  foot,  lateral  view     ......  192 

94.  Position  for  posterior  portion  of  os  calcis  ....  192 

95.  Resuscitation  from  electric  shock 200 


UNITED  STATES  ARMY 
X-RAY  MANUAL 


X-RAY    PHYSICS 

Introduction.— The  following  brief  notes  on  the  phys- 
ical aspects  of  the  apparatus  likely  to  be  used  in  military 
roentgenology  have  been  written  with  the  hope  that  their 
study  might  enable  the  roentgenologist  to  prepare  for 
service  in  less  time  and  be  better  able  to  utilize  the  appara- 
tus with  which  he  is  compelled  to  work.  With  the  belief 
that  brief  reasons  as  to  why  things  are  done  are  good 
guides  in  operation,  rather  more  explanation  of  fundamen- 
tal principles  has  been  given  than  is  usually  included. 

X-Rays.— The  roentgen  or  x-rays  are  produced  by  an 
electric  current  in  a  glass-walled  vacuum  tube.  Such  a 
current  is  due  to  the  projection  of  minute  electric  particles 
(electrons)  from  one  metal  terminal,  the  cathode,  to  an- 
other metal  terminal,  the  anode  or  target.  The  x-rays 
originate  at  the  point  of  impact  of  the  electrons  on  the 
target  and  travel  out  from  their  origin  in  all  directions 
except  where  dense  material  obstructs  or  prevents  their 
passage.  When  passing  through  bodies  made  up  of  various 
parts  differing  in  density,  some  of  the  rays  that  enter 
the  denser  portions  are  permanently  cut  out  and  a  new 
distribution  of  intensity  in  the  beam  results. 

The  presence  of  x-rays  must  be  determined  by  some  of 

15 


16  U.  S.  ARMY  X-RAY  MANUAL 

the  effects  they  produce  when  acting  on  material  bodies. 
These  actions  are : 

1.  Effect  on  the  emulsion  of  a  photographic  plate. 

2.  Excitation  of  light  in  certain  crystals  (fluorescence). 

3.  Rendering  gases  conducting  to  electricity  (ioniza- 
tion). 

4.  Stimulating  or  destructive  action  on  living  cells 
(biological  action). 

The  first,  second,  and  fourth  of  these  are  of  fundamental 
value  in  the  medical  and  surgical  uses  of  the  rays.  The 
third  has  been  very  useful  in  the  study  of  the  radiation. 

These  rays  do  not  excite  vision  on  reaching  the  retina 
of  the  eye,  but  are  capable  of  originating  light  in  cer- 
tain crystals.  A  uniform  beam,  falling  on  a  piece  of 
cardboard  covered  with  such  crystals,  would  cause  uni- 
form illumination.  If  regions  of  unequal  material  den- 
sity have  been  traversed  by  the  beam  before  reaching 
the  screen  (fluoroscope),  such  dense  portions  will  show 
as  areas  of  lesser  brightness  or,  as  we  say,  will  cast  shad- 
ows. In  the  same  way,  a  photographic  plate  or  film  suffi- 
ciently acted  upon  by  such  rays  will,  on  development,  give 
areas  of  unequal  blackening,  marking  out  the  projections 
of  volumes  in  the  body  whose  densities  differ  from  those 
surrounding  them.  On  the  fluoroscopic  screen,  dense  bodies 
show  as  dark  areas;  in  a  photographic  negative,  they  show 
as  light  areas. 

It  has  been  shown  by  various  investigations  that  x-raj^s 
are  identical  in  their  nature  with  light  and  electric  waves, 
except  that  their  wave  lengths  are  very  much  less  than 
even  the  shortest  light  waves.  On  account  of  this  ex- 
tremely short  wave  length,  the  effect  of  matter  upon  their 
propagation  is  quite  different  from  that  in  the  case  of 
longer  waves.  Such  short  waves  are  only  produced  by  a 
change  in  the  velocity  of  electrons  taking  place  in  intervals 


X-RAY  PHYSICS  17 

of  time  too  short  to  be  easily  conceived.  The  gamma 
rays  of  radium,  etc.,  are  simply  rays  due  to  the  sudden 
starting  out  of  electrons  by  atomic  breakdown.  They  may 
be  shorter  or  longer  than  the  x-rays  we  use  in  fluoroscopy 
or  in  radiography. 

The  term  ray  is  used  to  designate  two  distinct  types 
of  phenomena.  One,  a  projection  of  small  particles  by 
atomic  disintegration,  as  beta  and  alpha  rays.  The  other 
refers  to  the  transfer  of  physical  effects  by  the  agency  of 
wave  motion.  In  this  class  we  have  light,  gamma  and 
x-rays. 

It  may  be  also  noted  here  that  gamma  rays  are  of  the 
same  physical  nature  as  x-rays,  but  some  gamma  rays  are 
of  shorter  wave  length  than  the  x-rays  we  are  able  to  pro- 
duce at  the  present  time. 

The  following  general  properties  of  this  radiation  should 
be  understood  in  order  to  facilitate  its  intelligent  applica- 
tion. 

Paths. — These  rays  travel  in  straight  lines  into,  through, 
and  out  of  material  bodies,  except  where  the  atoms  them- 
selves cause  scattering.  They  cannot  he  directed  by  mir- 
rors or  lenses  for  purposes  of  optical  focus  or  concentra- 
tion, as  is  done  with  light.  The  slight  amount  of  regular 
reflection  by  the  uniformly  spaced  atoms  in  crystals  is 
too  small  to  be  of  any  importance  to  the  roentgenologist. 

Velocity. — The  rays  travel  out  from  the  target  at  the 
same  velocity  as  light  or  electric  waves. 

Energy. — The  actual  energy  involved  in  an  x-ray  beam 
is  small  compared  with  that  expended  in  getting  it  started ; 
only  a  few  parts  in  a  thousand  of  the  energy  supplied 
is  converted  into  x-rays. 

Scattering'. — ^X-rays  are  scattered  in  passing  through 
matter  exactly  as  light  is  scattered  in  turbid  water,  fog. 


18  U.  S.  ARMY  X-RAY  MANUAL 

paraffin,  etc.  Only  a  part  of  a  beam  is  thus  scattered, 
the  remainder  passing  straight  through  or  being  absorbed. 
Scattering  confuses  shadows  on  screen  or  plate  in  a  very 
troublesome  way. 

Passage  Through  Matter. — When  rays  pass  through  ma- 
terial, the  substance  is  called  transparent  to  the  radia- 
tion. If  little  or  no  radiation  gets  through,  we  say  the 
material  is  opaque  to  this  radiation.  The  terms  transpar- 
ent and  opaque  refer  to  the  action  of  the  material  with 
reference  to  a  specific  type  of  radiation.  If  one  arranges 
a  variety  of  substances  of  like  thickness  in  the  order  of 
increasing  density,  their  opacity  to  x-rays  will  be  nearly 
in  the  same  order.  But  this  will  vary  somewhat  according 
to  the  quality  of  the  x-ray  beam  considered.  That  portion 
of  the  incident  radiation  neither  transmitted  nor  scat- 
tered is  changed  into  heat  or,  as  we  say,  absorbed  in  the 
material.  We  then  say  that  absorbing  power  increases 
with  the  density  of  the  absorber.  This  absorbing  power 
is  best  expressed  as  the  fraction  of  the  rays  absorbed  by 
a  definite  thickness  of  material.  Thus,  if  1  cm.  of  water 
should  reduce  a  particular  radiation  so  that  the  emerging 
beam  is  half  as  effective  as  the  entering  one,  we  might 
say  this  radiation  has  a  half  value  layer  of  1  cm.  of 
water.  Two  centimeters  of  water  would  transmit  only  25 
per  cent  of  the  incident  beam  or  that  reaching  the  surface 
proximal  to  the  tube. 

The  quality  of  short  wave  length  and  high  penetration 
can  be  secured  only  by  means  of  high  voltage  operation. 
(See  penetration,  p.  46.) 

Electrons. — The  modern  concept  of  atoms  involves  the 
idea  of  their  general  electrical  constitution.  From  any 
atom  there  may  be  abstracted  one  or  more  small  negative 
charges,  all  precisely  alike,  whose  properties  are  in  no  wise 


X-RAY  PHYSICS  19 

dependent  on  the  atom  from  which  they  come,  and  all  are 
quite  capable  of  existence  by  themselves  without  the  pres- 
ence of  the  remainder  of  the  atom.  These  little  bodies  have 
been  variously  named  as  corpuscles,  cathode  rays,  beta 
rays,  electric-ions,  etc.  The  common  designation  of  elec- 
tron is  derived  from  the  latter.  An  electron  is  able  to 
respond  to  electric  force  and  to  acquire  velocity  under  such 
force  action.  When  in  motion,  they  show  all  the  charac- 
teristics of  an  electric  current. 

The  main  physical  features  of  electrons  are : 

1.  Their  fixed  and  definite  negative  charge. 

2.  Their  extremely  small  mass  and  volume. 

3.  The   extreme  speed   they   may   acquire. 

Production  of  X-Rays. — Roentgen  or  x-rays  originate  in 
any  region  where  the  velocity  of  electrons  is  suddenly 
changed.  In  the  radio-active  breakdown  of  atoms,  this 
change  is  a  sudden  acquisition  of  velocity,  and  the  gam- 
ma rays  are  produced.  In  x-ray  tubes,  the  high-speed 
electron  is  stopped  in  its  flight  by  the  interposition  of  a 
target  metal  of  high  atomic  weight  placed  in  its  path,  and 
x-rays  result  from  a  loss  of  velocity. 

The  problem  of  x-ray  production  for  our  purpose,  then, 
resolves  itself  into  four  parts. 

1.  The  separation  of  electrons  from  atoms. 

2.  Giving  them  high  speed. 

3.  Concentrating  them  on  a  small  area. 

4.  Stopping  them  with  sufficient  suddenness. 

The  first  of  these  is  accomplished  in  one  of  two  ways. 
In  the  tubes  containing  a  small  amount  of  gas,  electrons 
are  secured  in  part  by  high  electric  field,  but  to  a  much 
greater  extent  by  the  disruption  of  atoms  due  to  the  mov- 
ing electrons  and  by  the  x-rays  themselves.    In  the  more 


20  TJ.  S.  ARMY  X-RAY  MANUAL 

recent  hot  cathode  tube  (Coolidge),  electrons  are  set  free 
from  the  atoms  in  a  tungsten  wire  by  the  action  of  heat. 
In  the  former,  the  number  of  available  electrons  is  rather 
hard  to  control,  while  in  the  hot  cathode  tube  this  offers 
no  difficulty. 

In  order  to  secure  high  speed  (one-half  to  one-third 
the  velocity  of  light)  a  high  voltage  must  be  available, 
and  the  electrons  must  all  be  urged  toward  the  same  small 
area  in  order  to  get  sharp  shadows.  The  concentration 
on  the  target  is  secured  by  proper  design  of  the  elec- 
trodes and  their  proper  position  in  the  tube.  In  all  cases 
the  path  to  be  followed  must  be  quite  free  of  gas  in 
order  to  avoid  obstruction. 

The  choice  of  metal  as  a  barrier  is  of  great  importance, 
and  only  a  few  elements  satisfy  the  conditions.  Every 
fast-moving  electron  has  some  mechanical  energy  and  this 
goes  mainly  into  heat  by  impact;  there  results  a  great 
rise  in  temperature  at  the  point  of  electron  concentration. 
As  radiographs  and  fluoroscopic  images  are  purely  shadow 
effects,  a  source  of  radiation  starting  from  a  point  is  very 
desirable.  This  high  concentration  of  heat  will  melt  any 
target  material  at  high  power  operation.  Only  metals  of 
high  melting  points  can  be  utilized,  such  as  platinum, 
tungsten,  osmium,  and  iridium.  Of  these  the  first  two  are 
in  common  use,  the  tungsten  to  a  great  extent  during 
recent  years.  High  atomic  weight  is  also  desirable,  and 
fortunately  this  goes  with  high  melting  points  in  the  above 
metals. 

General  Instructions  and  Precautions. — 1.  Excessive  ex- 
posure to  x-rays  results  in  serious  injury  to  the  skin. 
Such  injury  does  not  manifest  itself  at  once  but  may 
develop  some  weeks  later.  To  a  degree,  the  action  is 
cumulative,  so  that  a  single  dose,  in  itself  too  small  for 


X-RAY  PHYSICS  21 

injury,  may,  when  frequently  repeated,  be  harmful.  Read 
carefully  the  notes  as  to  protection,  page  194.  While 
it  is  unwise  to  be  over  timid,  it  is  much  easier  to  prevent 
an  injury  than  to  cure  it. 

2.  X-ray  apparatus  is  expensive,  and  not  only  is  it 
costly  in  money  to  repair  damage,  but  even  more  impor- 
tant is  loss  of  service  from  breakdown.  Do  not  try  to 
see  how  much  current  you  can  pass  through  a  tube  or 
how  long  a  spark  the  transformer  will  give.  Do  not 
imagine  that  a  tungsten  target  cannot  be  melted;  it  can, 
and  very  quickly. 

3.  Acquire  the  habit  of  observing  whether  high  ten- 
sion wires  are  sufficiently  far  from  patient,  assistants, 
etc.,   before  you  close  the  operating  switch. 

4.  Make  all  tests  of  tubes,  etc.,  on  low  power,  when 
possible,  and  do  not  make  unnecessary  speed  your  ambi- 
tion. When  through  work,  throw  all  controls  to  low 
power. 

5.  Never  test  out  a  tube  when  the  patient  is  in  posi- 
tion. 

6.  Always  see  that  current  is  passing  through  the  fila- 
ment of  a  Coolidge  tube  before  closing  the  main  trans- 
former switch. 

7.  Do  not  imagine  you  can  make  plates  of  thick  parts 
on  very  low  spark  gaps.  It  cannot  be  done,  but  you 
may  get  some  very  unfortunate  experience  trying  it. 

8.  Remember  that  any  current  that  passes  across  the 
spark  gap  or  leaks  from  one  line  to  the  other  along  walls, 
etc.,  does  not  help  to  produce  x-rays,  although  it  may  in- 
crease your  milliammeter  reading. 

9.  Try  to  develop  a  definite  order  and  sequence  in 
the  various  details  of  any  examination.  It  will  save  time 
and  prevent  errors. 


22 


U.  S.  ARIVIY  X-RAY  MANUAL 


10.  The  only  safe  time  to  label  a  plate  or  film  for 
identification  is  at  the  time  of  exposure. 

11.  Don't  imagine  that  so  and  so's  good  plates  are 
due  to  the  particular  machine  he  is  using;  and  don't 
chase  off  after  every  new  exposure  "technique"  you  hear 
about.  The  fact  that  some  individuals  advocate  one  after 
another  is  ample  evidence  of  their  uselessness. 

Electrical  Terms. — Certain  terms  are  used  so  frequently 
in  all  discussion  of  electrical  matters  that  they  are  intro- 
duced at  this  point  for  convenience  in  reference. 

Charges. —  When  any  physi- 
cal or  chemical  action  breaks 
down  the  connection  between  an 
electron  and  the  remainder  of 
the  atom,  the  electron  consti- 
tutes the  elementary  particle  of 
negative  electricity.  All  nega- 
tive charges  are  simply  countless 
numbers  of  electrons  kept  away 
from  the  positive  portions  of  the 
atoms  from  which  they  were 
separated. 

Generators. — Generators  do 
not  create  electricity.  They 
take  electrons  and  positive  ato- 
mic remainders  apart  and  push  them  in  opposite  directions 
against  their  natural  tendency  to  keep  and  come  together. 
Thus,  if  G,  Fig.  1,  represents  a  generator,  A  and  B  metal- 
lic plates  connected  to  its  terminals,  A  is  covered  with  elec- 
trons and  B  with  enough  positive  to  neutralize  the  negative 
on  A.  If  we  call  e  the  negative  charge  of  one  electron,  and 
Q  the  total  charge  on  A,  N  the  number  of  electrons,  then  Q 
equals  Ne,  where  N  is  an  incredibly  large  number  in 
most  eases, 


Fig.  1.    Generator  on  open 
circuit. 


X-RAY  PHYSICS  23 

Voltage. — Electric  charges  separated  as  shown  in  Fig. 
1,  show:  (1)  a  mechanical  pull  on  the  bodies  A  and  B, 
(2)  a  decided  tendency  to  pass  between  A  and  B. 

A  voltmeter  does  not  measure  electricity  but  something 
like  a  pressure  or  strain  trying  to  pass  a  charge  between 
two  regions. 

The  Volt. — The  volt  is  the  unit  in  which  the  tendency 
of  charge  to  move  from  one  place  to  another  is  measured. 
The  electrical  tension  between  the  terminals  of  a  special 
cell  (Weston  or  Cadmium  cell)  is  taken  by  legal  definition 
as  1.019  volts. 

Current. — When  proper  external  connections  are  made 
to  the  terminals  of  a  generator  there  results  a  transfer 
of  charge.  If  we  could  count  the  number  of  electrons 
passing  on  to  A  per  second,  say  n,  we  would  call  ne  the 
current  passing  through  G.  An  electric  current  may  then 
be  regarded  as  a  measure  of  the  number  of  electrons  pass- 
ing per  second.  It  must  be  observed  that  after  A  and  B 
are  charged  as  highly  as  is  possible  for  the  particular  gen- 
erator, there  will  be  no  further  current,  but  the  voltage 
is  present.  We  may  have  voltage  existing  and  no  current, 
hut  never  a  current  without  some  voltage. 

The  Ampere. — The  ampere  is  the  unit  of  electric  cur- 
rent. It  is  legally  defined  as  the  rate  of  transfer  of  electric 
charge  which  deposits  silver  from  a  special  solution  at 
the  rate  of  .001118  grams  per  second.  The  unit  electric 
charge  is  the  coulomb.  Five  amperes,  for  example,  will 
transfer  40  coulombs  in  8  seconds. 

Resistance. — It  requires  but  little  voltage  to  move  a 
big  supply  of  electrons  through  some  materials,  while  with 
others  a  very  great  voltage  will  cause  but  little  electron 
movement.  The  former  are  named  conductors;  the  latter, 
insulators.     Note  carefully  that  the  difference  is  one  of 


24  U.  S.  ARMY  X-RAY  MANUAL 

degree,  and  that  perfect  insulators  do  not  exist  so  far  as 
high  applied  voltage  is  concerned.  Thus,  dry,  clean  glass 
may  be  considered  an  insulator  for  moderate  voltages, 
but  may  conduct  to  a  considerable  extent  at  high  voltage. 
The  objection  offered  to  the  passage  of  an  electric  current 
by  any  material  included  in  a  circuit  is  called  its  resist- 
ance. 

The  Ohm. — The  unit  of  electrical  resistance.  Legally 
defined  as  the  resistance  of  a  uniform  column  of  mercury 
106.3  cm.  long  and  one  square  millimeter  section  at  0° 
centigrade. 

Power. — The  ability  of  the  electric  current  to  do  work 
is  termed  its  power. 

The  Watt. — The  watt  is  the  unit  of  electrical  power. 
It  is  the  power  of  a  current  of  1  ampere  in  a  region  where 
it  loses  1  volt.  The  product,  amperes  x  volts  lost  =  power 
in  watts ;  746  watts  are  equivalent  to  one  mechanical  horse- 
power, and  1  kilowatt  is  therefore  equal  to  about  1%  horse- 
power. 

Derived  Units. — The  units  given  above  are  not  of  con- 
venient size  in  all  cases,  and  some  modifications  are  in 
common  use.  The  terminal  voltage  on  the  tube  is  high, 
and  it  is  often  expressed  in  kilovolts  (1  kilovolt  equals 
1000  volts).  The  current  ordinarily  used  through  x-ray 
tubes  is  small  and  is  expressed  in  milliamperes  (1  milli- 
ampere  equals  y-^^  ampere).  The  power  used  to  oper- 
ate electrical  devices  is  generally  expressed  in  kilowatts, 
when  the  number  of  watts  is  large  (1  kilowatt  equals 
1000  watts).  One  kilowatt  maintained  for  one  hour  is 
named  a  kilowatt-hour. 

As  applied  in  particular  cases,  a  4  kw.,  110  volt  gen- 
erator, is  a  machine  that  delivers  4000  watts  at  full  load 
and  is  designed  to  operate  at  110  volts.     The  full  load 


X-RAY  PHYSICS  25 

current  would  be  ^^-^-^  =  36.3  amperes.  If  a  machine 
gives  50  milliamperes  at  70  kilovolts,  the  power  delivered 
is  ^^^^  X  70  X  1000  ^  3500  watts,  or  31/2  kw. 

Measuring  Instruments. — The  electrical  measuring  in- 
struments that  may  concern  the  roentgenologist  are  the 
ammeter  and  the  voltmeter  for  low  tension  circuit Sf  the 
milliammeter,  and  the  kilovoltmeter  for  high  tension  cir- 
cuits. Most  kilovoltmeters  are  of  little  real  value  as  they  vary 
with  the  secondary  current.  The  milliammeter  is  a  most 
valuable  aid  to  the  work.     It  is  often  designed  for  two 

/<?  Ohms    Q 

— -^AA/WV^^^ 


Fig.  2.     Simple  electric  circuit. 

ranges.  From  0  to  15  ma.  on  one  scale  and  0  to  150  ma. 
on  the  other  is  the  best  for  most  work. 

Do  not  try  to  draw  150  ma.  when  the  meter  is  set  for 
a  maximum,  of  15  ma.  If  the  pointer  gets  bent,  due  al- 
lowance must  be  made  in  reading. 

Electric  Circuit. — An  electric  circuit  consists  of  some 
sort  of  a  generator  and  a  more  or  less  complex  conducting 
path  between  its  terminals.  Electricity  outside  a  gener- 
ator always  passes  from  high  to  low  voltage,  and  the  cur- 
rent may  properly  be  said  to  lose  voltage  en  route  from 
one  generator  terminal  to  the  other. 

Consider  a  very  simple  circuit,  Fig.  2,  consisting  of  a 
generator,  O;  generator  resistance  one-tenth  ohm,  two  other 


26 


U.  S.  AR]\iy  X-RAY  MANUAL 


resistances  as  shown.  The  fundamental  law  of  such  a 
circuit  is  that  if  when  the  switch,  S,  is  open  we  have,  say 
220  volts,  then  for  any  total  resistance,  B,  we  will  have 
a  current,  on  closing"  ^S',  such  that 

Current  x  total  resistance  =  220,  or  in  this  case, 
No.  of  amperes  x  (.1  +  .9  +  19)  =  220 
Current,  /  =  220  =11  amperes. 

20" 

The  voltage  is  used  up  as  follows: 

In   the     generator   11  x  .1  =      1.1  volts 
Between  A  and  B  11  x  19  =  209.0 
Between  B  and  C  llx  .9=     9.9 


Total 


220.0  volts 


Fig.  3.     Current-time  curve  of  a  simple  a.c.  circuit. 

This  relation  is  true  for  all  circuits,  viz.,  volts  lost 
due  to  resistance  of  B  ohms  when  a  current  of  I  amperes 
is  flowing  =  I  B. 

Direct  Current  (d.c). — When  the  electron-flow  is  in 
only  one  direction,  the  current  is  named  direct.  Dry  cells, 
storasre  batteries,  static  machines,  and  d.-c.  dynamos  deliver 


X-RAY  PHYSICS  27 

direct  current.  A  current  may  be  intermittent  or  pulsat- 
ing, and  still  be  called  a  direct  current. 

Alternating  Current  (a.c.). — ^When  the  electrons  flow 
in  one  direction  for  a  short  time  and  then  the  flow  de- 
creases and  a  reverse  flow  occurs,  we  say  the  current  is 
alternating.  A.-c.  dynamos  are  the  only  sources  of  true 
alternating  current. 

Such  a  current  in  its  simplest  form  may  be  pictured 
by  a  suitable  time-current  diagram.  In  Fig.  3  time  is 
shown  as  increasing  from  left  to  right. 

Let  OC  =  —  second 

60 


Then  OC  =BD  =CE  =P^  P^  =-^  second 

This  current  takes  all  its  variable  values  once  in  1/60 
of  a  second,  and  repeats  the  operation  60  times  in  one 
second.  It  is  designated  as  60  cycle  a.  c.  If  drawn  from 
a  220  volt  service,  its  complete  designation  is  220  volt — 
60  cycle — alternating  current  of  a  certain  number  of 
amperes. 

During  the  times  OB,  CD,  EF,  etc.,  current  flows  in  the 
opposite  sense  to  that  during  the  times  EC,  BE,  etc.  Note 
that  there  are  two  alternations  to  each  cycle,  or  120  per 
second  in  this  case. 

X-Ray  Current-Voltage  Requirements. — ^At  present  x- 
ray  tubes  are  used  with  currents  varying  approximately 
between  5  and  100  milliamperes,  and  at  voltage  running 
between  25  and  100  kv.,  i.  e.,  25,000  to  100,000  volts.  This 
high  voltage  requirement  cannot  be  met  by  simple  d.-c.  gen- 
erators. 

High  Voltage. — The  requisite  voltage  is  secured  by  the 
use  of: 


28  U.  S.  ARMT  X-RAY  MANUAL 

1.  The  so-called  static  machine  (direct  but  impractical). 

2.  The  periodic  interruption  of  a  direct  current  through 
one  coil,  causing  high  voltage  in  a  neighboring  coil  (in- 
duction coil). 

3.  Using  a  low  voltage  alternating  current  in  one  coil 
and  getting  a  high  voltage  alternating  in  an  adjacent  coil 
(transformer). 

The  second  device  is  still  used  to  some  extent,  but  has 
largely  been  displaced  by  the  transformer  in  recent  years. 
The  use  of  an  induction  coil  or  a  transformer  to  in- 
crease voltage  involves  two  distinct  circuits,  one  connected 
through  some  control  device  to  the  supply  line  or  genera- 
tor, and  known  as  the  primary  circuit ;  the  other,  insulated 
from  the  primary  and  connected  to  the  tube  terminals, 
known  as  the  secondary  circuit. 
The  primary  always : 

Is  of  relatively  low  voltage. 
Is  a  moderately  large  wire. 
Carries  a  current  of  some  amperes. 
Is  reasonably  safe  to  touch. 

Requires  good  metallic  contacts  at  all  connections. 
The  secondary  always: 
Is  high  voltage. 
Is  quite  a  small  wire. 
Carries  a  current  of  some  milliamperes. 
Is  unpleasant  and  often  dangerous  to  touch. 
"Will  pass  current  across  loose  connections  or  even 
through  some  insulating  material. 
The  induction  coil  and  a  few  transformers  have  both 
coils  wound  on  hollow  concentric  cylinders,  the  primary 
within  the  secondary,  and  the  space  inside  the  primary 
coil  is  filled  with  thin  iron  sheets  or  wires.     These  are 
named  open  magnetic  circuit  devices. 

Most  transformers  now  in  use  have  the  iron  in  the  form 


X-RAY  PHYSICS 


29 


of  a  closed  rectangle,  and  the  two  coils  wound  so  as  to 
slip  on  the  sides  of  this  rectangle.  These  are  known  as 
closed  magnetic  circuit  transformers. 

The  Gas  Tube. — While  a  great  variety  of  special  forms 
of  gas  containing  tubes  have  been  introduced  from  time 
to  time,  the  general  form  shown  in  Fig.  4  alone  has  sur- 
vived for  ordinary  use. 


1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 


Pig.  4.     Eegular  gas  containing  tube. 

Negative  or  cathode  terminal. 

Cathode  of  aluminum. 

Adjustable  connections  for  softening. 

Softening  material. 

Sealing  off  tip. 

Auxiliary  anode. 

Copper  block. 

Tungsten  button. 

Positive  or  anode  terminal. 

Anode  neck. 

Cathode  neck. 

Cathode  particles. 

Path  of  x-rays. 


A  L  M,  Anterior  hemisphere  showing  fluorescence. 


30 


U.  S.  ARMY  X-RAY  MANUAL 


The  target  material  lias  a  great  influence  on  the  be- 
havior of  the  tube  and  the  quality  of  the  rays.  The  atomic 
weight  must  be  high,  as  the  fraction  of  cathode  ray  energy 
traiisformed  into  x-rays  increases  with  increase  of  atomic 
weight.  The  melting  point  must  be  high  or  the  metal  will 
melt  at  the  focus.  It  should  conduct  heat  well,  and  must 
not  vaporize  readily  below  its  melting  point.  The  follow- 
ing table  gives  the  approximate  data  relating  to  possible 
metals  for  this  purpose.  Taking  platinum  as  a  standard 
radiator: 


Amount  of 

Metal 

At.  Wt. 

X-Radiat 

ion 

Melting  Pt, 

Platinum 

195.2 

1. 

1760.  C. 

Iridium 

193. 

.98 

2300 

Osmium 

190.9 

.97 

2700 

Tungsten 

184. 

.91 

above 

3000 

Tantalum 

181. 

.90 

2900 

The  essential  features  of  all  modern  tungsten  target  gas 
containing  tubes  are  shown  in  Fig.  4.  Various  minor 
modifications  may  be  seen  in  tubes  from  different  mak- 
ers, but  each  part  shown  must  be  present  in  some  form. 

The  cathodes  may  differ  in  shape,  but  only  aluminum 
nves  good  results  and  long  tube  life.  The  mounting  of 
cathode  and  target  must  be  firm,  and  the  position  in  the 
leck  carefully  chosen.  The  adjustable  arm  (3)  is  often 
absent,  and  a  third  wire  is  run  to  a  variable  spark  gap 
connecting  with  the  negative  terminal  of  the  machine. 
The  auxiliary  anode  (6)  has  a  great  variety  of  forms; 
in  many  water-cooled  tubes,  and  sometimes  in  others  (6) 
and  (10)  are  interchanged.  Numerous  special  devices  for 
conducting  heat  away  from  the  target  are  in  use  and  are 


X-RAY  PHYSICS  31 

more  or  less  effective.  For  treatment  or  for  long  fluoro- 
scopic examination  with  this  type  of  tube,  water  cooling 
is  essential,  and  a  good  stream  of  air  directed  against  the 
glass  adjacent  to  the  cathode  is  also  of  considerable  as- 
sistance. A  satisfactory  tube  must  have  a  stable  position 
of  anode  and  cathode;  all  attempts  to  use  an  adjustable 
cathode  have  been  unsatisfactory.  The  metal  parts  must 
be  pre-heated  and  the  tube  itself  heated  during  exhaustion. 
A  well  made  and  properly  exhausted  tube  shows  a  good 
hemisphere  on  the  anterior  portion,  and  the  remainder  of 
the  tube  should  show  but  little  fluorescent  light ;  a  working 
tube  should  not  be  ''flashy"  or  ''cranky."  When  one 
attempts  to  operate  a  moderately  hard  tube  at  too  low 
potential,  this  unstable  state  may  result  and  either  the 
voltage  must  be  raised  or  the  tube  softened.  The  vacuum 
must  be  within  fairly  well-defined  limits,  averaging  not 
far  from  .001  mm.  pressure  of  mercury,  and  must  be 
in  some  manner  under  control,  if  the  life  of  the  tube  is 
of  consequence. 

The  tendency  of  all  gas  containing  tubes  on  low  current 
is  to  "harden,"  i.  e.,  to  require  more  voltage  for  the  same 
current,  or,  if  the  voltage  is  not  changed,  the  current  de- 
creases. On  operation  above  a  certain  power  peculiar  to 
each  tube,  the  tube  softens  on  account  of  heating;  when 
this  proceeds  so  far  that  the  tube  shows  and  maintains 
a  purple  glow  marking  out  the  cathode  stream,  it  is 
useless  until  repumped. 

Many  devices  have  been  used  to  soften  tubes.  The  more 
common  are  the  following: 

1.  A  side  tube  containing  mica,  asbestos,  etc.,  and 
through  which  a  small  discharge  current  may  be  sent, 
thereby  liberating  gas.     (No.  4,  Fig.  4.) 

2.  A  special  target  is  placed  in  a  side  tube  to  be  bom- 
barded by  rays  from  a  small  auxiliary  cathode. 


32  U.  S.  ARMY  X-RAY  MANUAL 

3.  A  fine  palladium  tube  projects  througli  the  walls 
of  the  tube;  when  this  is  heated  by  a  small  flame  it 
allows  hydrogen  to  pass  into  the  bulb.  This  has  been  modi- 
fied by  Snook,  where  the  tube  is  heated  by  a  spark  dis- 
charged from  the  operating  transformer. 

4.  Heating  the  entire  bulb.  (Useless  except  in  an 
emergency.) 

5.  A  mercury-controlled  porous  valve  allows  air  to  pass 
slowly  into  the  bulb  when  the  inlet  is  not  covered  by  the 
mercury  (Heinz-Bauer). 

2,  3,  and  4  are  rarely  used  in  this  country,  although  3 
(osmosis  regulators)  are  sometimes  seen  outside  the  more 
useful  Snook  form. 

The  Coolidge  Tube. — The  great  difficulty  in  the  opera- 
tion of  the  ordinary  gas  containing  tube  lies  in  the  ir- 
regular supply  of  electrons  and  the  impossibility  of  control 
of  their  development.  When  operated  above  very  mod- 
erate power,  the  trend  is  always  toward  larger  quantities 
of  electrons  and  a  consequent  drop  in  penetration,  unless 
the  current  is  greatly  increased,  when  a  still  greater  sup- 
ply is  developed,  so  that  there  is  no  automatic  self-pro- 
tection of  the  tube. 

Wehnelt  found  that  a  platinum  ribbon  coated  with  lime 
would  allow  of  current  transfer  through  a  high  vacuum 
at  moderate  voltages.  Several  attempts  to  use  such  a 
cathode  for  x-ray  tubes  were  unsuccessful,  and  no  modifi- 
cation of  the  standard  tube  appeared  until  it  was  found 
by  Richardson  and  others  that  electrons  were  emitted 
by  hot  metals. 

The  simplest  application  of  this  principle  to  x-ray  de- 
velopment has  been  worked  out  by  Dr.  "W.  D.  Coolidge  in 
the  Research  Laboratory  of  the  General  Electric  Company 
at  Schenectady.  In  this  tube,  the  cathode  is  a  spiral 
filament  of  tungsten  wire,  A,  Fig.  5,  heated  to  a  high  tern- 


X-RAY  PHYSICS 


33 


perature  by  a  current  from  an  insulated  storage  battery, 
or  by  a  special  transformer.  The  form  of  electrostatic 
field  needed  for  focussing  the  electron  stream  is  fixed  by  a 
small  molybdenum  cylinder,  B,  within  which  the  cathode 
is  placed.  The  target  is  usually  a  solid  piece  of  wrought 
tungsten  mounted  on  a  molybdenum  rod,  around  which 
collars  are  placed  to  distrib- 
ute the  heat  conducted  from 
the  target. 

Fig.  6  shows  the  Coolidge 
tube. 

1.  Cathode  terminal. 

2.  Electron  focusing  cone,  struction. 

3.  Solid  tungsten  target. 

4.  Molybdenum  supporting  rod. 

5.  Anode  terminal. 

In  order  to  operate  properly,  it  was  found  that  the 
highest  possible  vacuum  must  be  attained.  Not  only  was 
the   greatest   care   required   in   pumping,   but  the   metal 


Fig.  5.     Coolidge    cathode    cort- 


Fig.  6.     Coolidge  tube. 

parts  had  to  be  freed  from  occluded  gas  by  heating  in  a 
vacuum  nearly  to  their  melting  point.  In  this  tube  there 
is  no  source  of  electrons  except  from  the  hot  filament, 
and  as  this  supply  depends  only  on  the  temperature  of 
the  filament,  the  operator  has  perfect  control  of  the  num- 
ber of  available  electrons  by  simply  changing  the  auxiliary 


34 


U.  S.  ARMY  X-RAY  MANUAL 


current.  A  small  transformer  is  now  generally  used  to 
supply  low  voltage  for  the  filament  current.  Connections 
are  as  shown  in  Fig.  7.  The  winding  connected  to  the 
filament  must  be  well  insulated  from  case  and  primary 
winding. 

The  current  through  the  tube  cannot  be  increased  after 


FILRMBNT 


ZSO  VOLTS 


Fig.  7.     Wiring  diagram  for  step-down  transformer  to  supply  cur- 
rent for  filament  of  Coolidge  tube. 


the  supply  of  electrons  is  entirely  utilized,  no  matter  how 
much  the  voltage  is  raised.  This  maximum  current  for 
each  particular  filament  temperature  is  named  the  saturor 
tion  current,  and  until  this  is  reached  the  voltage  main- 
tained between  cathode  and  target  may  be  too  low  for 
use.  So  long  as  the  negative  current  reaching  the  tube 
does  not  exceed  the  number  of  electrons  emitted  per  sec- 


X-RAY  PHYSICS  35 

ond  multiplied  by  the  charge  of  each  electron,  there  can  be 
no  charge  piled  up  on  the  electrodes — i.  e.,  no  effective 
terminal  voltage. 

No  Inverse. — ^A  further  valuable  feature  of  the  tube 
is  its  inability  to  transmit  inverse  so  long  as  the  focal  spot 
is  not  too  hot.  On  account  of  the  increased  strain  on 
the  glass,  v^hen  inverse  is  present,  it  is  well  to  include 
a  valve  tube  v^hen  operating  on  a  heavy  coil. 

Penetration  Limits. — The  highest  operating  voltage  on 
the  present  tubes  is  about  100  kv.,  as  measured  on  a  spe- 
cial electrostatic  voltmeter.  This  refers  to  ' '  effective ' '  volt- 
age; the  peak  voltage  is  larger  than  this. 

No  doubt  this  can  be  increased  by  modification  of  the 
design,  but  insulation  difficulties  and  danger  of  puncture 
v^ill  be  increased  as  higher  voltages  are  used.  Such  high 
penetrating  rays  as  may  now  be  reached  are  not  useful  in 
fluoroscopic  work  or  in  radiography,  partly  on  account  of 
the  enormous  amount  of  scattered  radiation  developed  in 
the  tissues  of  the  body.  Such  scattered  and  corpuscular 
rays  may,  however,  be  useful  in  therapeutic  work.  Very 
soft  rays  may  be  produced  in  great  abundance  if  the  glass 
will  allow  them  to  pass  out.  Attempts  to  use  too  soft  rays 
in  radiographic  work  are  always  fraught  with  grave  dan- 
ger. 

No  Fluorescence  in  the  Glass. — In  marked  contrast  to 
the  usual  tube,  there  is  no  fluorescence  of  the  glass  walls 
except  a  slight  illumination  in  the  anode  neck.  Some- 
times a  minute  chip  in  the  glass  or  a  slight  evolution  of 
tungsten  vapor  will  give  a  momentary  flash  of  green,  but 
on  further  operation  at  moderate  power  this  disappears. 
The  bombardment  of  the  walls  of  the  tube  by  electrons 
reflected  from  the  target  or  scattered  from  the  gas  atoms 
in  the  gas  containing  tube  is  the  cause  of  the  fluorescence 
and    of    a    very    considerable    amount    of    soft   radiation 


36 


U.  S.  ARMY  X-RAY  MANUAL 


originating  in  the  glass.  As  there  is  in  a  gas  tube  as  large 
a  supply  of  positive  ions  as  of  negative,  continual  recom- 
bination results,  and  no  negative  layer  can  form  on  the 
glass  walls  to  prevent  bombardment  by  scattered  and  re- 
flected electrons.  In  the  Coolidge  tube  the  absence  of  posi- 
tive ions  probably  allows  the  accumulation  of  a  negative 
charge  on  the  glass,  and  as  soon  as  established  this  layer 
repels  electrons  and  the  glass  is  no  longer  a  target. 

New  Form  of  Coolidge  Tube. — The  ordinary  form  of 
Coolidge  tube  will  operate  satisfactorily  without  a  rectifier 
if  the  focal  spot  is  at  a  temperature  "below  that  at  which  it 
gives  off  an  appreciable  numher  of  electrons.  It  follows 
that  part  of  the  problem  of  eliminating  the  rectifier  is  keep- 


I 


i 


Tig.  8.    Eadiator  type  of  Coolidge  tube. 


ing  the  target  cool.  A  new  form  of  tube  which  will  help 
greatly  in  this  mode  of  operation  has  recently  been  de- 
veloped by  the  General  Electric  Research  Laboratory,  Fig. 
8.  The  target  is  a  tungsten  button  set  in  a  heavy  copper 
backing  which  is  continuous  with  a  large  copper  rod  ex- 
tending out  of  the  tube  neck.  To  this  are  attached  a 
series  of  discs  acting  as  radiators.  Operated  within  limits 
set  by  the  manufacturers,  this  tube  suppresses  completely 
each  alternate  half  wave  and  may  be  operated  direct  on  a 
suitable  transformer.  At  present  these  are  designed  for 
10  ma.  at  a  5-inch  gap  for  radiographic  work,  and  for 
5  ma.  at  the  same  gap  for  continuous  duty  in  fluoroscopy. 
The  wiring  diagram  then  becomes  very  simple  and  easily 
understood. 


X-RAY  PHYSICS 


37 


In  Fig.  9  are  shown  a  current-time  curve  and  a  voltage- 
time  curve  for  the  self-rectifying  tube.  In  the  latter  OA 
is  the  v^^orking  peak  voltage  which  determines  the  tube 
radiation,  and  BC  is  the  peak  voltage  of  the  suppressed 
wave  which  would  give  the  spark  gap  reading. 

A  transformer  should  be  used  which  will  not  vary  its 


iA_„A„..A_.A 


TIME 


Fig.  9.  Current  and  voltage  curve  for  self -rectifying  Coolidge 
tube.  The  voltage  difference  indicated  by  the  excess  of  BC  over  OA 
will  depend  on  design  of  transformer  and  controL 

voltage  too  much  from  no  current  to  that  needed  to  oper- 
ate it  properly,  since  the  voltage  of  the  suppressed  wave 
is  quite  decidedly  higher  than  that  of  the  one  used,  there- 
by causing  spark-over  and  giving  an  incorrect  idea  of  the 
actual  working  voltage. 

The  value  of  this  arrangement  for  field  work  can  hardly 
be  overestimated,  as  there  is  no  heavy  and  complicated 
rectifier.     Operated  from  a  small  gas  engine-driven  gen- 


38  U.  S.  ARMY  X-RAY  MANUAL 

erator,  it  is  ideal  for  fluoroscopic  work  and  satisfactory  for 
emergency  radiography.  See  U.  S.  Army  Portable  Unit, 
page  167. 

Tube  Focus. — The  x-rays  cannot  be  focussed  by  any 
known  method,  so  that  the  terms  focal  point,  etc.,  are  mis- 
leading. Electrons  can  be  directed  by  suitable  cathode 
construction  so  that  the  greater  portion  strike  a  small  area 
on  the  target.  The  diameter  of  this  area  is  known  as 
the  *' focus,"  and  it  is  customary  to  speak  of  broad,  me- 
dium, and  fine  foci.  One  can  hardly  state  precise  limits 
between  these  designations,  but  anything  below  3  mm. 
would  be  extra  fine  focus ;  3  to  4  mm.  fine  focus ;  4  to  7  mm. 
medium  focus;  and  over  7  mm,  broad  focus. 

The  size  of  focus  is  found  by  the  use  of  a  pin-hole  cam- 
era, and  should  be  given  by  the  maker.  Its  size  is  im- 
portant in  two  ways :  First,  in  relation  to  the  sharpness 
of  image  on  plate  or  screen;  second,  as  fixing  the  power 
that  may  be  used  without  damage  to  the  target.  "When  an 
electron  stream  is  maintained  at  high  velocity  against  the 
target,  there  is  a  rapid  rise  in  temperature  which  may 
result  in  vaporization  or  fusion  of  the  metal.  The  rate 
of  removal  of  heat  by  conduction  is  increased  by  broaden- 
ing the  focal  spot,  and  the  amount  of  metal  suffering 
extreme  rise  in  temperature  is  increased,  so  that  for  two 
reasons  there  is  less  danger  of  target  damage. 

The  effect  on  sharpness  of  image  is  shown  by  using  an 
exaggerated  diagram  as  in  Fig.  10.  Fi  F^  are  the  bound- 
aries of  the  focal  spot  and  1-2  is  the  object.  "With  the 
plate  in  plane  A,  had  the  only  source  been  a  point,  F^,  a 
sharp  shadow  PQ  would  result;  had  F2  been  the  only 
source,  then  BS  would  result.  The  only  portion  entirely 
shaded  is  BQ,  and  if  the  object  is  round,  we  have  a  cen- 
tral white  spot  with  a  variable  shading  out  to  a  diameter 
PS.    If  the  focal  spot  were  very  wide  and  the  object  very 


X-RAY  PHYSICS 


39 


small  a  plane  B  could  be  found  beyond  which  there  would 
be  no  white  image. 

The  ring  PE  and  Q8  is  narrower  the  closer  the  object 
to  the  plate,  the  smaller  the  focal  spot  and  the  greater 
the  target-plate  distance.  The  apparent  size  of  the  shadow 
will  vary  somewhat  with  exposure,  as  regions  partly  shaded 
may  be  under-exposed  when  the  exposure  is  brief  and  the 
true  shadow  may  not  appear  at  all. 


Fig.  10.     Variation  of  size  of  shadows  of  small  objects  when  a  wide 
focus  is  used  close  to  the  plate. 


Fine  focus  tubes  are  not  needed  in  gastro-intestinal 
work,  and  should  be  used  in  other  work  with  such  care 
that   the   target   does  not  become   pitted. 

Conditions  for  Operation. — Two  things  must  be  consid- 
ered in  the  operation  of  x-ray  tubes.  The  first  is  a  proper 
supply  of  electrons  as  current  carriers,  the  second  a  proper 
electric  drive  to  force  these  electrons  against  the  target. 
These  two  must  be  so  related  to  each  other  that  a  proper 
voltage  can  be  maintained  when  current  is  actually  used. 

No  amount  of  milliamperage  will  serve  to  do  radiographic 
or  fluoroscopic  work  without  a  proper  voltage  consumption 


40  U.  S.  AR]\iY  X-RAY  MANUAL 

at  the  tube.  The  potential  difference  or  voltage  drop 
across  the  tube  is  due  to  a  piling  up  of  positive  charges 
and  electrons  at  the  target  and  cathode  respectively  and 
this  must  be  done  by  the  generator.  When  electrons  move 
across  from  cathode  to  target  they  tend  to  relieve  the  con- 
gestion and,  if  the  generator  should  fail  to  maintain  the 
supply,  the  voltage  and  charge  would  disappear.  The  great- 
er the  number  of  electrons  passing  across  in  a  given  time, 
the  more  the  terminal  voltage  will  be  reduced  for  a  given 
ability  of  the  generator  to  pump  a  new  supply.  The 
current  is  the  charge  of  one  electron  multiplied  by  the  num- 
ber passing  per  second.  Hence  the  greater  the  milliamper- 
age,  the  greater  the  power  demanded  from  the  generator 
to  maintain  voltage  and  the  more  the  drop  in  voltage 
from  that  shown  on  open  circuit  or  on  small  current. 

When  the  current  increases,  irrespective  of  the  type  of 
tube  used  or  the  design  of  the  machine,  the  operating 
voltage  will  be  reduced  unless  the  rheostat  or  autotrans- 
former  control  is  moved  to  apply  more  power  to  the  pri- 
mary. The  spark  gap  on  open  circuit  is  no  guide  to  the 
ability  of  the  transformer  or  induction  coil  to  keep  up 
voltage  when  current  is  drawn. 

Inasmuch  as  reduced  voltage  very  much  more  than  off- 
sets the  effect  of  change  of  current  in  x-ray  production 
as  regards  quantity,  and  likewise  decreases  the  ability  to 
pass  through  material,  the  proper  maintenance  of  volt- 
age is  the  most  indispensable  requisite  in  any  x-ray  instal- 
lation. By  increasing  exposure  time  nearly  all  work  may 
he  properly  done  at  low  current,  hut  no  increase  of  expo- 
sure time  will  compensate  for  too  low  voltage. 

The  transformer  must  be  designed  for  the  voltage  supply 
on  which  it  is  used,  and  it  is  very  essential  that  the  proper 
terminal  voltage  on  the  transformer  primary  should  be 
maintained  at  all  times  and  at  all  loads.    After  a  machine 


X-RAY  PHYSICS  41 

is  once  installed  the  operator  has  no  control  over  these 
matters.  The  size  of  wire  required  to  transmit  current 
from  the  usual  power  transformer  to  the  x-ray  room  will 
depend  on  the  distance  between  the  two  transformers  and 
on  the  voltage  used.  To  transmit  the  same  power  at  110 
volts  as  at  220  will  require  twice  the  current.  Whenever 
a  given  current  is  passed  over  a  resistance  there  is  a  volt- 
age drop  or  loss.  This  loss  is  greater,  the  greater  the  cur- 
rent and  the  greater  the  resistance.  "When  the  line  resist- 
ance and  the  current  are  known  the  voltage  loss  is  found 
by  taking  their  product.  A  loss  of  2  or  3  per  cent  of  the 
line  voltage  may  be  permissible.    See  line  wiring,  p.  70. 

The  operator  must  take  care  that  the  current  through 
the  tube  does  not  drop  the  potential  too  much  for  the 
work  required.  For  increased  tube  current  the  rheostat 
or  autotransformer  setting  must  be  raised  accordingly. 

Gas  Tube  Characteristics. — The  earlier  type  of  tube  de- 
pended for  its  supply  of  electrons  on  the  breakdown  of  the 
atoms  of  its  gaseous  atmosphere,  whereby  the  electrons  and 
the  positive  remainder  of  the  atom  were  separated  and 
driven  in  opposite  directions.  This  breakdown  or  ioniza- 
tion may  be  due  to  several  causes : 

1.  The  high  electric  stress  between  cathode  and  target. 

2.  The  shooting  of  electrons  through  the  atmosphere. 

3.  The  passage  of  x-rays  through  the  atmosphere. 

The  number  of  electrons  set  free  will  depend  on  the  tube 
vacuum.  If  too  few  can  be  had,  the  tube  is  of  too  high 
vacuum  and  is  called  ''hard."  It  backs  up  a  very  high 
spark  gap,  and  may  become  "cranky."  If  too  much  gas 
is  present  the  tube  carries  so  much  current  that  it  is 
quite  impossible  to  keep  up  voltage.  The  amount  of 
free  gas  in  the  tube  will  increase  as  the  parts  of  the  tube 
rise  in  temperature,  since  gas  tends  to  stick  to  a  cold 


42  U.  S.  AR]\iY  X-RAY  MANUAL 

surface.  Therein  often  lies  the  explanation  of  failure 
in  radio^aphy  on  prolonged  exposure. 

The  rate  of  softening  of  a  gas  tube  operated  at  a  given 
initial  current  and  voltage  varies  with  its  original  ex- 
haustion and  its  use  afterward.  On  low  power  with  small 
current  and  high  voltage  there  is  a  marked  tendency  to 
reduce  the  amount  of  free  gas  and  thus  raise  the  vacuum. 
When  this  tendency  is  just  balanced  by  the  evolution  or 
release  of  gas  by  heat  the  tube  runs  at  a  nearly  uniform 
current  and  voltage.  On  slightly  higher  power  it  will 
soften  and  the  rate  of  softening  will  generally  be  greater 
with  a  new  tube  than  in  case  of  a  well-seasoned  one. 

Danger  in  Testing*. — It  is  unwise  to  test  a  gas  tube  at 
the  power  used  in  gastro-intestinal  or  other  heavy  work, 
as  it  is  likely  to  over-soften  before  a  milliammeter  can  be 
read  or  spark  gap  really  ascertained.  The  usual  recourse 
is  to  note  current  and  gap  at  low  power,  and  assume 
that  when  this  is  properly  adjusted  on,  say,  button  X, 
it  will  give  a  proper  result  on  a  higher  button  Y.  Careful 
study  of  these  tubes  shows  that  this  is  only  approximately 
the  case,  for  not  only  will  tubes  vary  one  from  another, 
but  the  same  tube  will  behave  differently  on  different 
days.  No  better  method  has  been  suggested,  however, 
so  the  operator  should  endeavor  to  season  a  tube,  if  pos- 
sible, before  attempting  fast  work. 

Coolidge  Tube  Characteristics. — The  electron  supply  in 
the  Coolidge  type  of  hot  cathode  tube  is  due  entirely  to 
the  hot  tungsten  filament,  as  all  the  gas  it  is  possible  to 
remove  has  been  taken  out  in  pumping.  The  current  car- 
ried by  the  tube  is  limited  by  the  rate  of  electron  supply 
and  is  thus  determined  solely  by  the  filament  current. 
This  maximum  tuhe  current  at  a  given  filament  current  is 
only  attained  at  a  sufficiently  high  voltage  and  this  voltage 
increases  as  the  filament  temperature  is  raised.    When  all 


X-RAY  PHYSICS 


43 


the  electrons  are  being  driven  across  as  fast  as  they  are 
produced,  the  corresponding  current  is  named  the  satura- 
tion current.  After  such  a  current  is  reached  the  voltage 
may  be  greatly  increased  v^ithout  a  rise  in  tube  current. 
Fig.  11  shows  this  characteristic  of  the  tube,  quite  different 
from  the  gas-containing  tube  where  higher  applied  voltage 


.  Fig.  11.     Current-voltage  lines  of  Coolidge  tube  for  fixed  filament 
temperatures.     Vertical  portions  are  above  ''saturation"  points. 


brings  increased  current.  On  account  of  the  great  increase 
of  tube  current  resulting  from  a  slight  rise  in  filament 
current  the  writer  has  found  it  impractical  to  depend  on 
the  filament  ammeter  as  a  guide  to  tube  current,  especially 
when  using  rheostat  control.  In  fact  better  work  is  done 
where  no  dependence  is  put  on  anything  except  spark  gap 
and  tuhe  current. 

Outflow  of  Radiation. — As  radiation  proceeds  from  the 
origin  on  the  target  it  spreads  out  and  flows  through  the 


44  U.  S.  AEMY  X-RAY  MANUAL 

surfaces  of  larger  and  larger  spheres.  The  amount  re- 
ceived in  a  given  time  by  any  fixed  area  then  decreases 
as  the  distance  of  the  receiving  surface  is  greater.  This 
decrease  always  follows  the  inverse  square  law.  Thus  if 
100  arbitrary  units  reach  a  given  area  at  10  inches  from 
the  target,  the  same  area  20  inches  from  the  target  will 
only  get  1/4  as  much  in  the  same  time,  i.  e.,  25  units.  At 
30  inches  the  sam^e  area  receives  but  1/9  as  much  or 
11  1/9  units.  Or  to  get  the  same  radiation  to  this  area  at 
the  increased  distances  the  time  must  increase  as  the  square 
of  the  distance,  i.  e.,  if  at  15  inches  2  seconds  are  re- 

—  j    =  2  X  -—   ,  at  25  inches 

2  X   —  ,  at  30  inches  2x    j---jc=2x4  =  8  seconds, 

etc. 

Amount  of  Radiation. — The  measurement  of  x-ray  radi- 
ation has  proved  a  rather  difficult  matter  and  need  not 
be  fully  discussed  here.  For  our  purpose  the  photographic 
measure  is  sufficiently  accurate  and  determines  the  useful- 
ness of  the  rays  in  practice.  "Whatever  the  conditions  of 
operation,  we  might  take  a  time  of  exposure  so  as  to  get 
the  same  blackening  on  two  spots  on  a  photographic  plate, 
and  then  say  that  the  two  had  the  same  exposure,  when 
exposure  does  not  mean  time  of  tube  action  alone. 

Such  a  method  measures  only  the  effect  of  rays  used  in 
changing  the  emulsion,  not  the  total  beam,  the  greater 
portion  of  which  passes  through  the  film. 

Quality. — Fully  as  important  as  the  amount  of  radiation 
is  the  quality  or  distribution  of  radiation  among  various 
wave  lengths.  Quality  determines  the  ability  of  the  rays 
to  pass  through  flesh  and  bone,  and  was  roughly  gauged 
by  the  use  of  penetrometers.  It  depends  on  the  voltage 
used  to  drive  the  current  across  the  space  between  cathode 


X-RAY  PHYSICS  45 

and  anode,  and  is  best  expressed  in  terms  of  voltage  or 
gap. 
Dependence  of  Quantity  on  Electrical  Conditions. — It 

is  very  important  to  realize  that  the  amount  of  radiation 
as  measured  by  the  photographic  effect  is  simply  related  to 
the  electrical  conditions  under  which  a  tube  is  operated. 
If  we  let   I  =  Current  in  milliamperes 
Y  =  Effective  voltage  in  kv. 
Then  radiation  leaves  the  target  at  a  rate  depending  on 
the  product  of  current  and  the  square  of  the  voltage.    The 
amount  reaching  a  given  area  placed  at  right  angles  to 
the  flow  and  at  a  distance  d  from  the  target  and  in  a  time 

t  is  measured  by  — ^7-- 

Thus  if  7i,  =  40  ma.,  V^  =  30  kv.,  d  =  20  inches,  t  = 
1  second,  in  one  case,  and 

Jg  =  10  ma.,  V2  =  60  kv.,  d  =  20  inches,  #  =  1  second 
in  another,  then  Q^  =  40x30x30x  1/400  =  90  arbitrary 
units  where  Q^  =  amount  of  radiation  in  the  first  case 
and  O2  =  10x60x60x1/400  =  90  units  in  the  second 
case.  That  is,  40  ma.  at  30  kv.  and  10  ma.  at  60  kv. 
will  produce  the  same  quantity  of  x-rays  as  measured 
by  photographic  effect. 

However,  the  radiation  produced  at  60  kv.  is  better  able 
to  penetrate  any  piece  of  matter,  and  a  higher  percentage 
passes  through,  so  that  a  plate  exposed  partly  to  one  and 
partly  to  the  other  through  a  block  of  material  will  show 
much  more  darkening  for  the  second  case,  even  though 
the  quantities  of  radiation  generated  at  the  tube  are  equal. 
It  would  darken  the  plate  equally  if  no  body  were  inter- 
posed. 

No  matter  what  amount  of  current  is  passed  through 
a  tube  it  is  useless  for  radiographic  or  fluoroscopic  work, 
unless  a  voltage  able  to  break  down  from.  3  to  6  inches 


46 


U.  S.  ARMY  X-RAY  MANUAL 


of  air  between  hlwnt  points  is  used.  For  thick  parts  the 
higher  voltage  (gap)  must  be  used. 

The  relation  of  sparking  distance  (between  blunt  points) 
to  kilo  volts  is  shown  in  Fig.  12.  The  kilovoltage  is  approxi- 
mately ten  times  the  gap  in  inches  plus  ten. 

Penetration. — The  most  characteristic  feature  of  x-rays 


0        iO     20     30     40     50     60     70     60     dO    100 

K.V. 

Fig.  12.     Approximate    relation    between    effective    kilovolts    and 
spark  gap  for  moderately  blunt  points. 

is  their  ability  to  pass  through  material  quite  opaque  to 
other  types  of  radiation.  In  all  cases  there  is  some  absorp- 
tion, but  the  rate  of  absorption  or  the  amount  left  after 
passing  through  any  layer  of  material  varies  according  to 
the  composition  of  the  x-ray  beam.  The  most  penetrat- 
ing rays  are  produced  only  at  higher  voltages.  This  pene- 
tration could  be  accurately  defined  in  the  case  of  a  beam  of 
one  wave  length,  but  it  is  quite  difficult  in  the  case  of  an 
actual  complex  beam. 


X-RAY  PHYSICS  47 

It  is  essential  for  the  operator  to  realize  that  increas- 
ing the  tube  voltage  will  (a)  add  shorter  and  more  pene- 
trating rays;  (b)  increase  the  quantity  of  the  less  pene- 
trating which  were  produced  at  the  lower  voltage. 

X-Ray  Transformer. — There  is  no  practical  means  of 
directly  generating  an  electric  current  at  the  voltage 
needed  in  the  production  of  useful  x-rays,  hence  it  is  nec- 
essary to  use  a  transformer,  stepping  up  low  voltage  cur- 
rent to  the  high  voltage  required.  The  transformer  consists 
of  two  coils  of  wire  around  a  common  iron  core.  For  com- 
plete insulation  of  the  coils  from  each  other  the  system  is 
immersed  in  oil  or  in  wax.  If  in  the  latter,  it  is  shipped 
complete;  when  oil  insulated,  the  oil  is  usually  shipped 
separately.  In  this  case,  it  should  be  siphoned  into  the 
transformer;  the  inlet  side  should  be  raised  an  inch  or 
so  to  get  complete  expulsion  of  the  air.  It  is  well  to 
operate  at  a  low  power,  allowing  sparks  to  pass  across  an 
inch  gap  for  some  time  to  dislodge  small  air  bubbles  be- 
fore putting  it  into  service. 

Use  no  oil  not  furnished  for  the  purpose  by  a  reliable 
manufacturer;  the  oil  must  contain  no  moisture. 

Examine  the  oil  level  every  two  months  to  be  sure  it 
fills  the  tank.  An  exposed  coil  is  sure  to  break  down 
hy  puncture  of  the  insulation.  The  top  of  the  case  should 
be  kept  free  from  oil  and  dirt.  For  protection  against 
surges  or  sudden  high  tension  pulses  which  are  likely  to 
damage  the  transformer,  a  resistance  should  be  placed 
in  shunt  with  the  low  tension  terminals.  If  this  is  not 
provided  by  the  maker,  ordinary  lamps  may  be  used.  Fig. 
13. 

The  middle  of  the  secondary  is  usually  connected  to  the 
case  (grounded)  ;  this  insures  a  distribution  of  potential 
equally  above  and  below  the  ''earth"  potential.  Thus,  if 
the  terminal  voltage  is  40,000  volts,  then  the  tendency  to 


48 


U.  S.  ARMY  X-RAY  MANUAL 


pass  a  spark  to  any  grounded  conductor  is  20,000  volts. 
This  arrangement  avoids  in  some  measure  the  tendency  to 
discharge  to  patient,  stand,  and  tube  that  would  result  if 
the  full  terminal  voltage  were  effective  to  earth. 

Care  must  be  taken  to  keep  all  contacts  on  the  low  volt- 
age side  tight.  See  that  low  tension  wires  are  kept  as  far 
away  from  the  high  tension  terminals  as  possible.  If 
trouble  actually  occurs,  due  to  short  circuit  or  break  inside 


Fig.  13.     Protection  from  surge  by  use  of  a  lamp. 


the  transformer,  there  is  no  use  in  trying  to  repair  it,  as 
a  rule,  unless  the  trouble  is  close  to  the  terminals.  If 
there  is  trouble  arising  from  sparking  across  between  the 
high  tension  terminals  of  the  transformer,  attaching  small 
spheres  will  relieve  the  tension  and  usually  cure  the 
trouble,  or  insulating  barrier  plates  may  be  used. 

Control  of  the  Transformer. — Corresponding  to  each  of 
the  various  high  tension  voltages  maintained  at  the  tube 
terminals,  there  must  be  applied  a  definite  voltage  across 
the  primary  of  the  transformer.  The  transformer  changes 
voltage  approximately  in  the  ratio  of  number  of  turns  in 
the  primary  to  number  of  turns  in  the  secondary,  and 


X-RAY  PHYSICS  49 

changes  current  in  the  inverse  ratio.  Thus  a  particular 
x-ray  transformer  might  be  wound  with  500  turns  in  the 
secondary  for  each  turn  of  primary,  and  it  would  be 
said  to  have  a  step-up  ratio  of  500.  The  secondary  volt- 
age would  be  500  times  the  voltage  in  the  primary  and  the 
secondary  current  1/500  of  that  in  the  primary. 

A  table  of  the  voltages  that  must  be  supplied  and  main- 
tained at  the  primary  terminals  to  give  various  high  tension 
voltages  can  easily  be  made  in  this  case. 


Primary 

Eesultant 

Spark  Gap 

Applied  Voltage 

H.  T.  Voltage 

(approximate) 

80  V. 

40  kv. 

3       in. 

90 

45 

31/2 

100 

50 

4 

110 

55 

41/2 

120 

60 

5 

130 

65 

51/2 

140 

70 

6 

150 

75 

61/2 

160 

80 

7 

220 

110 

10 

Such  primary  voltages  can  be  secured  from  a  line  sup- 
ply of  220  volts  (a)  by  the  use  of  a  rheostat,  (b)  by  the 
use  of  an  autotransformer. 

Rheostat. — The  rheostat  is  an  adjustable  resistance  used 
to  consume  a  part  of  the  line  voltage  and  leave  the  proper 
voltage  to  be  applied  at  the  transformer.  Suppose,  for 
instance,  it  is  desired  to  have  40  ma.,  at  a  5-inch  gap 
delivered  to  the  tube.  The  primary  must  be  supplied  with 
120  volts  and  a  current  of  40  ma.  x  500  =  20  amperes. 
In  this  case  the  rheostat  must  consume  100  volts  from  the 
220  volt  line  with  a  20  ampere  current.   Fig.   14.     By 


50 


U.  S.  ARMY  X-RAY  MANUAL 


Ohms  law  {V  =  IB)  the  voltage  consumed  in  the  flow  of 
current  through  a  resistance  is  equal  to  the  product  of  the 
current  in  amperes  and  the  resistance  in  ohms.  There- 
fore, 100  V  ^  20  X  B  from  which  i^  =  5  ohms,  hence  we 
would  need  5  ohms  of  the  rheostat  to  get  the  setting 
desired. 

The  rheostat  consists  of  coils  of  resistance  wire  con- 
nected end  to  end,  one  end  of  the  series  being  perma- 
nently  connected   to   one   wire   of  the   power   line.     Re- 

^ESISWATCE 

Hmmm 


^ /OOVr 


s 


± 


Fig.  14.     Diagram  showing  consumption  of  voltage  by  primary  of 
x-ray  transformer  and  series  resistance  for  a  particular  case. 

sistance  wire  is  made  of  some  special  material  of  con- 
siderably higher  resistance  for  the  same  diameter  and 
length  than  copper.  An  adjustable  contact  is  used  to  join 
one  transformer  terminal  to  any  desired  point  of  the 
rheostat  so  as  to  include  the  required  amount  of  resist- 
ance in  the  circuit.  Fig.  15  shows  the  essential  parts  of  a 
rheostat. 

The  usual  numbering  makes  the  power  increase  as  the 
control  lever  is  moved  over  to  higher  numbers.  A  good 
rheostat  should  be  of  substantial  construction,  well  ven- 
tilated, and  of  such  current  capacity  as  not  to  get  over- 
heated under  any  operating  conditions.     It  should  be  so 


X-RAY  PHYSICS 


51 


graded  as  to  give  30  to  70  ma.  on  a  4-inch  to  7-inch  gap  for 
radiographic  work  and  from  3  to  5  ma.  on  a  9  or  10-inch 

gap  for  treatment.  . 

The  use  of  a  rheo-  Transformer-^ 

stat  to  control  tube 
voltage  has  the  disad- 
vantage that  slight  va- 
riations in  tube  cur- 
rent result  in  serious 
changes  in  voltage.  To 
see  how  different  tube 
currents  cause  such 
enormously  different 
voltages  on  the  same 
control  setting,  let  us 
first  construct  a  table 
to    give    the    primary 

currents  corresponding  to  different  tube  currents.     Each 
primary  current  is  500  times  the  corresponding  secondary. 


Fig.  15.     Rheostat  construction  and 
connections. 


Secondary  Current 

Primary  Current 

0  ma. 

0  amps. 

10 

5 

20 

10 

40 

20 

60 

30 

80 

40 

100 

50 

Assuming  the  setting  of  5  ohms  resistance,  let  us  see 
how  the  voltage  applied  at  the  transformer  varies  under 
different  loads.  The  voltage  consumed  in  the  rheostat 
is  V  ^=  I R,  where  /  is  primary  current  and  R  is  constant 
at  5  ohms. 


52 


U.  S.  ARMY  X-RAY  MANUAL 


Secondary 
Current 

Primary 
Current 

Voltage 
Consumed 

in 
Rheostat 

Voltage 

left  over 

to  apply 

at  primary 

Resulting 

secondary 

voltage 

0  ma. 

0  amp. 

0  V. 

220  V. 

110  kv. 

10 

5 

25 

195 

97 

20 

10 

50 

170 

85 

40 

20 

100 

120 

60 

60 

30 

150 

70 

35 

80 

40 

200 

20 

10 

100 

50 

250 

These  figures  are  represented  graphically  in  Fig.  16. 
This  results  in  the  theoretical  chart  line  corresponding  to 
operation  on  the  particular  rheostat  control  button  se- 
lected. For  simplicity,  no  account  has  been  taken  in  these 
figures  of  line  wire  resistance,  resistance  in  the  windings 
of  the  transformer,  ' '  magnetic  leakage, ' '  and  other  factors 
which  enter  to  a  greater  or  less  degree. 

The  voltage  "regulation"  under  various  loads  of  a 
rheostat  controlled  transformer  is  poor.  On  any  one  con- 
trol setting  the  voltage  will  fall  off  very  rapidly  with  an 
increase  in  current,  and  rise  rapidly  with  a  decrease.  In 
Fig.  16  at  60  kv.  and  40  ma.  an  increase  of  8  ma.,  due 
to  softening  of  a  gas  tube  during  exposure  or  to  fluctua- 
tion in  the  filament  temperature  of  a  Coolidge  tube,  will 
lower  the  voltage  10  kv.,  or  about  an  inch  of  spark  gap. 
The  loss  in  voltage  and  penetration  will  have  considerably 
more  influence  on  a  plate  than  the  increase  in  current. 
Also,  if  there  were  a  break  in  the  Coolidge  filament  line,  or 
polarity  were  wrong,  so  that  no  current  flowed  in  the  sec- 
ondary circuit  the  primary  voltage  would  rise  to  that  of  the 
line  with  considerable  likelihood  of  sparking  to  the  patient 
or  causing  damage  to  apparatus. 

Auto  Transformer. — To    secure    better    voltage    main- 


X-RAY  PHYSICS 


53 


tenance  under  varying  loads  an  autotransformer  is  often 
used.  It  consists  of  a  continuous  coil  of  wire  wound  around 
an  iron  core  with  taps  taken  out  to  control  buttons  at 
proper  intervals,  as  shown  in  Fig.  17.    If  alternating  cur- 


liO 


KV 


100 

so 

60 

10 
60 
SO 
40 
30 
BO 
10 


^^^p{q:fff|4^4T}_iqqq::^"!"""""":"^"":"' 

"  L 

__\ X lii: — 

5  J -t -j-f -. 

'     L 

\ 

T                                                                                                                                                                                                                           I 

"■■"""              E                                                                                                                                             [^ 

■~              ^  ^ 

I  [                                                                                                                                          -t~ 

^ 

5- q- 

?^ -L 

^  L 

~                                   * 

5t 1 1 

Ik 

' — *. 

3^ i"+ 

5- 

'  ^ 

3^ 

_ ^- 

J  L 

i^ 

L 

"                                                                           *  I 

3| 

L 

"                                                                                                             *  ^ 

+ -J- "t- :- 

i -^- 

-             -                                           -             -^ 

10   20  30  40 


60  eo 
MR 


w  60  eo  100 


Fig.  16.  Theoretical  chart  line  plotted  from  data  given  in  table 
on  page  52.  This  line  shows,  for  the  particular  machine  and  set- 
ting, the  voltage  at  which  various  currents  will  be  delivered. 

rent  be  applied  to  the  complete  winding  of  such  a  coil  there 
will  be  a  voltage  induced  in  any  part  of  the  winding,  bear- 
ing the  same  relation  to  the  applied  voltage  that  the  num- 
ber of  turns  of  this  part  of  the  winding  bears  to  the  num- 
ber of  turns  in  the  whole  coil.  It  is  essentially  the  same  as 
any  other  transformer,  except  that  primary  and  secondary 


54 


U.  S.  ARMY  X-RAY  MANUAL 


are  part  of  the  same  continuous  wire  rather  than  separate 
windings,  and  its  action  depends  on  self-induction  in  a  sin- 
gle coil  rather  than  on  mutual  induction  between  two  coils. 
The  ratio  between  the  number  of  turns  in  the  primary  and 
secondary  circuits  is  changed  by  setting  the  control  lever 


Fig.  17.     Wiring  diagram  of  auto  transformer.     Notice  dead  but- 
tons between  the  active  ones  which  are  numbered. 


on  the  various  buttons.  The  autotransformer  is  used  as  a 
control  device  to  reduce  the  line  voltage  to  that  which  is 
applied  to  the  x-ray  transformer  primary,  hence  it  is  a 
step-down  transformer  and  has  fewer  turns  in  the  sec- 
ondary circuit  than  in  the  primary.  As  the  control  handle 
is  moved  to  higher  readings,  more  turns  are  cut  into  the 
secondary   circuit   and  higher  voltage   is   applied   to   the 


X-RAY  PHYSICS  56 

primary  of  the  x-ray  transformer.  Blank  or  ''dead"  but- 
tons are  placed  between  adjacent  live  buttons,  which  differ 
from  each  other  by  a  few  volts,  to  prevent  a  short  circuit 
of  this  low  voltage  by  the  control  lever  being  in  contact 
with  two  live  buttons  at  one  time. 

The  autotransformer  is  more  suitable  than  a  variable 
ratio  step-down  transformer,  which  might  be  used,  since 
it  saves  wire  and  iron,  being  much  smaller  for  equivalent 
capacity,  and  therefore  cheaper  to  build.  The  autotrans- 
former principle  cannot  be  applied  to  x-ray  and  filament 
transformers  because  their  ratio  is  too  large  and  the  pri- 
mary and  secondary  must  be  insulated  from  each  other. 

The  autotransformer,  like  an  ordinary  transformer,  is 
very  efficient  and  does  not  change  electric  energy  into  heat 
like  the  rheostat.  The  windings  are  of  large  copper  wire, 
with  low  ohmic  resistance.  When  increased  current  is  de- 
manded from  an  autotransformer,  it  simply  draws  more 
current  from  the  supply  line  and  delivers  the  current  de- 
manded with  very  little  drop  in  voltage. 

When  increased  current  is  demanded  in  the  tube,  it  will 
be  supplied  by  an  autotransformer  with  far  less  voltage 
drop  than  is  the  case  with  the  rheostat.  Fig.  18  shows  the 
behavior  of  the  two  devices  on  a  particular  machine.  Start- 
ing at  10  ma.  and  60  kv.,  and  raising  the  tube  current  on 
a  fixed  rheostat  setting,  gives  the  series  of  currents  and 
voltages  shown  by  the  line  AC;  while  on  a  fixed  autotrans- 
former setting  we  have  the  line  AB.  Since  the  quantity  of 
radiation  (measured  photographically)  increases  as  the 
current  and  the  square  of  the  voltage,  we  may  compute  the 
relative  amount  of  radiation  regardless  of  penetration. 
Curve  DE  shows  the  rheostat  delivery  down  as  low  as  use- 
ful rays  are  produced ;  DF  shows  the  delivery  on  the  auto- 
transformer up  to  60  ma. 

This  form  of  control  is  of  special  value  when  the  fila- 


56 


U.  S.  ARMY  X-RAY  MANUAL 


ment  current  of  a  Coolidge  tube  is  not  entirely  steady. 
Thus,  if  the  tube  current  in  the  case  cited  changed  from 
10  to  15  ma.,  with  a  rheostat  control,  the  radiation  would 
be  reduced  in  quantity  from  32  to  25  arbitrary  units  and 
also  would  be  much  less  penetrating;  while  with  the  auto- 
transformer  the  same  change  would  result  in  an  increase 


0         10     ZO     60    40     50     60     70     SO    10     100 

Fig.  18.  Eelation  of  x-ray  production  on  two  types  of  control. 
On  rheostat  control  we  have  AC  as  the  voltage- current  line.  Voltage 
ordinates  at  the  left.  BE,  corresponding  x-radiation  quantity,  ord- 
inates  at  the  right.  AB,  autotransformer  chart  line.  I>F,  corre- 
sponding quantity  line.    Quantity  in  arbitrary  units. 


in  quantity  from  32  to  50  units  very  slightly  less  pene- 
trating than  at  10  ma. 

"Inductance"  Taps. — Instead  of  controlling  completely 
by  variation  in  the  applied  voltage,  in  some  instances  the 
winding  ratio  of  the  x-ray  transformer  is  variable  by  a 
dial  switch  which  cuts  in  more  or  less  turns  of  the  trans- 
former primary.  The  lowest  ratio  of  step-up  corresponds 
to  the  complete  primary  and,  since  the  secondary  winding 


X-RAY  PHYSICS  57 

is  fixed,  to  cut  out  turns  of  the  primary  will  increase  the 
step-up  ratio  and  give  higher  secondary  voltage.  As  usual- 
ly applied,  the  machine  has  essentially  a  rheostat  control, 
with  rheostat  rather  than  autotransformer  characteristics, 
and  usually  more  taps  are  made  in  the  winding  than  serve 
a  useful  purpose. 

The  same  principle  is  conveniently  applied  in  transform- 
ers built  to  operate  on  either  220  or  110  volt  mains,  half 
as  many  primary  turns  being  used  for  110  volts  as  for 
220.  The  bedside  unit  uses  this  principle  for  110  volt  a.c. 
and  the  lower  voltage  a.c.  obtained  from  the  rotaiy  con- 
verter. In  some  instances  the  primary  is  wound  in  two 
sections  which  are  connected  in  series  for  220  volts  and  in 
parallel  for  110  volts,  in  the  latter  case  giving  carrying 
capacity  for  the  heavy  primary  currents  as  well  as  the 
higher  step-up  ratio. 

Transformer  Chart. — A  proper  procedure  in  handling 
machine  and  tube  is  indispensable.  Such  a  method  should 
be  adopted  as  will 

1.  Save  time  and  tubes. 

2.  Render  reproduction  of  results  possible. 

3.  Apply  to  all  machines. 

4.  Require  a  minimum  amount  of  instrument  reading 
when  operating. 

5.  Indicate  the  working  range  of  the  machine. 

The  working  spark  gap,  with  moderate  sized  blunt  points 
for  a  gap,  varies  from  about  3  inches  to  6  inches,  and 
currents  vary  from  5  to  100  milliamperes  in  fluoroscopic 
and  radiographic  work.  Any  possible  combinations  on 
the  machine,  giving  settings  outside  these  limits,  are 
practically  useless. 

On  any  transformer  outfit  find  first  a  5  ma.  6-inch  gap 
setting,  then  a  40  or  50  ma.  6-inch  gap  or  an  80  ma.  4-inch 
erap  sett  in  sr.     Studv  no  settiners  outside  these  limits.     In 


58 


U.  S.  ARMY  X-RAY  MANUAL 


Fig.  19  take  rheostat  setting  G  as  an  example.  Bead  the 
current  through  the  tube  when  a  6-inch  gap  just  fails  to 
hreak  (25  ma.).  Record  your  isetting  and  the  current. 
Leaving  the  x-ray  transformer  control  unchanged  find  the 
tube  current  at  which  a  5-inch  gap  just  fails  to  break. 
Do  the  same  for  a  4-  and  for  a  3-inch  gap.  When  these 
readings  are  plotted  to  scale,  as  in  Fig.  19,  they  should 


0         /O      20     30     40     50     60     70     80     fO     100 

flA. 

Fig.  19.  Partial  **eharf  of  a  particular  machine  with  rheostat 
control.  Note  that  gap  change,  as  tube  current  increases,  is  very- 
rapid.  On  G,  for  example,  we  have  a  6-ineh  gap  at  25  ma.  and  only 
a  5-inch  gap  at  27.5  ma.  or  a  change  of  an  inch  for  each  2^2  ma. 
Compare  with  Fig.  20. 


fall  nearly  on  a  straight  line.  If  they  do  not  do  so,  repeat 
the  observations. 

So  long  as  the  power  supply  is  kept  at  the  voltage  pre- 
vailing when  this  chart  was  determined  the  coordinates  of 
a  line  give  all  the  currents  and  voltages  at  any  time  avail- 
able on  the  indicated  rheostat  setting.  H  gives  the  currents 
at  which  gaps  between  6  and  3  inches  are  broken  on  button 
H.  Fig.  20  shows  five  such  lines  for  a  particular  machine 
on  autotransformer  control. 

How  to  Use  the  Chart. — Using  chart,  Fig.  19,  one  needs 


X-RAY  PHYSICS 


59 


for  a  particular  case  20  ma.  at  a  4-inch  gap.  The  vertical 
line  through  20  cuts  the  line  marked  F  at  the  4-inch  gap. 
Hence  we  must  use  button  F.  Have  spark  gap  open  to 
seven  or  eight  inches  as  a  safety  valve  and  forget  it  en- 
tirely. Move  rheostat  lever  to  F,  look  at  your  milliamme- 
ter,  use  one  hand  on  transformer  primary  switch  and  the 
other  on  the  Coolidge  control.  Close  transformer  switch 
and  bring  filament  control  to  a  setting,  giving  20  milliam- 


^  10     ZO     30     40     so     60     70     60     90     lOQ 

Fig.  20.  Partial  ''chart"  of  the  same  transformer  using  auto- 
transformer  control.  Note  that  line  marked  P  shows  all  useful  cur- 
rents that  can  be  had  on  this  setting:  changing  from  5  ma.  to  50  ma. 
lowers  gap  from  5  to  3  inches. 

peres  tube  current;  there  is  no  need  of  testing  the  spark 
gap. 

Do  not  try  to  read  the  milliammeter  on  the  throw. 
Learn  to  start  and  set  your  machine  within  10  seconds. 
On  20  ma.  desired,  a  current  of  19  or  21  ma.  is  close  enough 
for  this  work. 

Using  chart,  Fig.  20,  for  45  ma.  at  a  4-inch  gap,  go  at 
once  to  E  and  proceed  as  before.  A  little  time  spent  in 
making  this  chart  and  in  using  it  will  reduce  time  lost 
and  failures.  Note  that  the  faster  the  spark  gap  falls  with 


60 


U.  S.  ARMY  X-RAY  MANUAL 


Main     cr] 


t 


increase  of  tube  current  the  more  accurately  must  the  fila- 
ment current  be  adjusted  and  maintained. 

Synchronous  Motors. — ^A  synchronous  motor  is  one  that 
makes  either  the  same  number  of  revolutions  per  minute  as 
the  generator  feeding  it  or  a  fixed  fraction  thereof.  Thus, 
if  fed  by  a  60  cycle  alternating  current,  there  are  7200 
alternations  per  minute.  One  alternation  is  produced  when- 
ever a  conductor  passes  one  pole  piece  of  the  generator. 
Thus,  a  60  cycle  current  from  an  eight-pole  machine  requires 

900  r.p.m  (revolu- 
tions per  minute), 
since  7200  =  8  x  900. 
For  a  four-pole  ma- 
chine we  must  have 
1800  r.p.m.,  etc.  A 
four-pole  motor  must 
then  make  1800  r.p.m. 
for  synchronism  if  on 
such  a  circuit,  and  it 
must  not  make  1801 
or  1799.  Since  the 
rectifier  for  a  60  cy- 
cle current  must  make  a  quarter-turn  each  1/120  of  a  sec- 
ond, the  motor  must  turn  at  1800  r.p.m.  It  must  be  ob- 
served that  such  a  motor  is  designed  for  a  given  fre- 
quency and  cannot  be  expected  to  work  on  one  greatly 
different  from  that  intended. 

Starting*. — Many  motors  require  connection  to  a  special 
starting  device  in  order  to  bring  them  up  nearly  to  the 
required  speed  before  making  the  running  connection. 
Do  not  delay  too  long,  and  do  not  throw  over  the  switch 
too  quickly.  A  little  practice  will  enable  you  to  tell  by  the 
sound  of  the  machine  when  the  speed  is  about  right. 
Polarity  Indicator. — Some  machines  have  a  field  wind- 


L=^ 


Main 


CO 


I 


Fig.  21.    Wiring  of  * '  polarity ' '  switch. 


X-RAY  PHYSICS 


61 


ing  which  ensures  the  same  terminal  polarity  each  time 
the  machine  is  started.  In  most  machines  there  is  as  much 
chance  of  a  given  terminal  starting  -f  as  — .  Polarity  in- 
dicators are  often  used  to  show  which  way  the  rectifier 
comes  into  step.  Either  a  primary  reversing  switch,  Fig. 
21,  is  used  or  the  motor  switch  is  opened  for  an  instant 
and  again  closed,  thus  allowing  the  motor  to  drop  back  with 


WSULfiTOR  SEGMENT 


jfEdiermcE 

Fig.  22.     Principle  of  polarity  indicator.    Note  resistance  in  series. 

the  chance  of  changing  polarity  of  the  high  tension  lines. 
These  indicators  are  devices  to  indicate  direction  of  cur- 
rent flow,  used  in  connection  with  a  small  low-tension  rec- 
tifier driven  by  the  motor.  In  Fig.  22  a  source  of  alter- 
nating current  is  obtained  from  the  primary  lines;  C  is  the 
low  tension  rectifier,  or  commutator,  fastened  on  the  same 
shaft  as  the  high  tension  rectifier,  and  I  is  the  indicator. 
The  direction  of  the  rectified  current  through  the  indi- 
cator circuit  will  be  one  way  or  the  other,  depending  on 
how  the  two  rectifiers  happen  to  come  into  step.    The  indi- 


62 


U.  S.  ARMY  X-RAY  MANUAL 


cator  itself  consists  of  a  movable  coil  with  pointer  attached, 
working  against  a  hair-spring  in  a  permanent  magnetic 
field,  and  it  is  very  similar  in  construction  to  a  direct  cur- 
rent voltmeter  or  ammeter.  If  the  rectified  current  flows 
one  way  through  the  coil,  the  needle  will  be  deflected  to 
on  side;  if  the  current  flows  in  the  reverse  direction,  the 
needle  will  swing  to  the  opposite  side. 


Fig.  23.     Principle  of  rotary  converter   showing  two  positions  of 
active  coil  180°  apart,  armature  current  being  always  alternating. 


The  indicator  is  usually  of  low  resistance  with  an  auxil- 
iary resistance  unit  included  in  the  circuit  to  prevent  burn- 
out of  the  indicator  coil.  Never  connect  the  indicator  with- 
out this  resistance  in  circuit,  and  in  testing  to  find  the 
proper  connections  always  use  a  lamp  in  series  with  the 
indicator  to  prevent  burnout,  if  connection  is  accidentally 
made  to  too  high  voltage. 

Rotary  Converter. — If  the  line  supply  is  direct  current 
it  must  be  changed  into  alternating  by  means  of  a  rotary 


X-RAY  PHYSICS  63 

converter,  since  the  x-ray  transformer  will  operate  only 
when  its  primary  is  supplied  with  alternating  current. 
The  operation  of  the  converter  is  based  on  the  fact  that  the 
current  flowing  through  the  armature  of  a  direct-current 
motor  is  alternating.  To  simplify  explanation,  consider  the 
case  of  a  machine  having  two  field  poles  and  a  single  arma- 
ture coil.  At  the  left,  Fig.  23,  are  the  brushes  to  which  the 
direct  current  line  is  connected,  and  at  the  right  those  from 
which  the  alternating  current  is  drawn.  The  flow  of  cur- 
rent through  the  armature   coil   in  the  direction  of  the 

VOJJS y.^220D.C. 


Fig.  24.     Eelation  between  d.e.  voltage  supplied  and  a.c.  voltage 
delivered. 

pointers  causes  rotation  of  the  coil  as  indicated,  owing  to 
the  reaction  with  the  magnetic  field  between  the  stationary 
pole  pieces.  When  the  coil  has  rotated  just  beyond  the  ver- 
tical plane  the  connection  of  the  rotating  commutator  seg- 
ments with  the  d.-c.  feed  brushes  is  reversed,  the  current 
through  the  armature  coil  is  reversed,  and  rotation  is  there- 
by made  to  continue.  Each  half  revolution  of  the  armature 
causes  a  reversal  of  current  through  the  armature  winding 
and  a  change  in  polarity  of  the  two  segments.  If,  now, 
these  segments  are  continuously  connected  to  the  same 
collector  brushes  by  means  of  slip  rings,  the  current  drawn 
from  these  brushes  will  be  alternatingr  current. 


64  U.  S.  ARMY  X-RAY  MANUAL 

The  direct-current  voltage  supplied  to  the  rotary  con- 
verter corresponds  to  the  peak  voltage  of  the  alternating 
current  wave,  and  the  effective  voltage  of  the  alternating 
current  is  only  about  70  per  cent  of  this,  Fig.  24.  Thus  a 
converter  operating  on  220  volts  d.c.  will  deliver  only  154 
volts  a.c.  and  if  220  volts  a.c.  are  required,  it  is  necessary 
to  step  up  by  means  of  a  special  transformer  or  autotrans- 
former.  Under  heavy  load  the  voltage  will  fall  considerably 
below  the  70  per  cent,  and  serious  difficulties  will  arise 
from  trying  to  use  a  rotary  converter  too  small  for  the 
demands  placed  upon  it. 

In  direct-current  x-ray  machines  the  rotary  converter 
drives  the  rectifying  device.  In  this  case,  the  machine  al- 
ways starts  up  with  the  same  high  tension  polarity,  and  a 
polarity  indicator  or  polarity  switch  is  unnecessary.  If 
polarity  is  wrong  permanently,  interchange  the  primary 
lead  wires  at  the  transformer  or  reverse  the  tube  in  the 
stand. 

In  using  a  rotary  converter,  one  should  remember  that 
all  the  power  used  passes  into  the  rotary  through  the  d.-c. 
brushes,  and  all  used  by  the  x-ray  transformer  passes  out 
from  the  slip  rings.  In  the  a.-c.  machine  the  transformer 
power  does  not  pass  through  the  motor,  so  that  greater 
care  of  brushes,  etc.,  is  needed  in  the  d.-c.  machine. 

A  considerable  proportion  of  failures  of  rotaries  is  due 
to  the  breakdown  of  insulation  at  the  connection  of  the 
armature  wires  to  the  slip  rings.  * '  The  Care  of  Motors ' '  on 
page  84  applies  also  to  rotary  converters.  Protection 
should  be  made  against  high  tension  surges  by  connecting 
an  incandescent  lamp  across  the  a.-c.  end,  as  is  done  to 
protect  a  transformer.  Fig.  13. 

Rectifier. — Two  forms  of  rotating  circuit  changers  are 
in  common  use,  the  cross-arm  type  and  disc  type.  Both  are 
run  by  a  synchronous  motor,  and  they  must  be  correctly 


X-RAY  PHYSICS 


65 


placed  relative  to  the  motor  armature  if  efficient  delivery 
is  to  be  secured.  Fig  25  shows  the  current  path  for  the 
four-arm  type,  Fig.  26  for  the  two-arm,  and  Fig.  27  for 
the  disc  type. 

In  Fig.  25  when  the  right  hand  terminal  of  the  trans- 
former is  -,  the  flow  of  negative  charge  or  of  electrons  is 
from  A-B-iuhe-C-D.  If  the  spindle  turns  90°  while  the 
polarity  of  the  transformer  is  reversed,  electrons  flow  from 


— 7^ — T"*" 


Fig.  25.     Secondary  circuit  of  Fig.  26.     Second  circuit  Waite 

gnook  machine.     Cross-bar  type      &    Bartlett    machine — cross-arm 
j-ectifier — four  arms.  type — two  arms. 


E-F-tuhe-G-H.  In  both  eases  the  current  takes  the  same 
direction  through  the  tube. 

The  disc  type  is  shown  in  Fig.  27.  PQ  and  RS  are  two 
conducting  sectors  fastened  to  an  insulating  disc  turned  by 
the  motor. 

Flow  is  A-B-tuhe-C-D  in  one  case  and  a  quarter  turn 
connects  D  to  B  and  C  to  A.  Meanwhile  the  transformer 
has  reversed  so  that  electrons  pass  from  D-B-tuhe-C-A. 

In  Fig.  25  the  cross-arm  machine,  E  and  A,  C  and  F,  B 
and  G  must  be  well  insulated  by  barriers,  or  else  the  shaft 
must  be  unduly  long.  In  the  disc  machine  the  diameter 


66 


U.  S.  ARMY  X-RAY  MANUAL 


must  be  large  enough  to  insure  insulation  between  the  shaft 
and  the  rim  and  also  to  avoid  establishing  an  arc  between 
the  fixed  sectors  along  the  edge  of  the  disc. 

Sparking-  Troubles. — Dust  and  moisture  may  impair  the 
insulation  of  the  barriers  or  disc.     Keep  them  clean  and 
wipe  with  a  cloth  slightly  moistened  with  kerosene. 
The  cross-arm  type  must  be  well  insulated  where  the 

arms  pass  through  the 
shaft.  If  a  break  occurs 
there,  it  is  not  possible  to 
patch  it  up.  Get  a  new 
cross-arm. 

Noise. — If  a  disc  is  out 
of  balance  or  if  the  bear- 
ings are  worn  by  lack  of 
lubrication  a  machine  will 
be  noisy.  Be  sure  to  keep 
bearings  well  oiled.  Do 
not  accept  a  machine  poor- 
ly balanced. 

Inverse. — Inverse  shows 
by  fluorescent  rings  back 
of  the  target  in  a  gas  tube  and  by  sparks  across  gap  on 
low  power  setting  on  Coolidge  tube.  It  is  caused  by  recti- 
fier out  of  position.  It  is  assumed  that  the  maker  will 
mark  the  shaft  of  the  cross-arm  type  or  the  disc  in  the 
other  class  with  reference  to  the  motor  shaft  so  that  one 
can  see  if  slip  has  taken  place  and  adjust  to  the  proper 
position.  If  this  has  not  been  done,  readjust  so  that  the 
current  is  a  maximum  on  a  low  power  setting  and  with 
the  tube  kept  constant.  This  is  fairly  easy  with  a  Coolidge 
tube.  One  accustomed  to  the  appearance  of  the  arcs  at 
the  rectifier  terminals  can  set  fairly  accurately  by  obser- 
vation. 


Fig.  27.     Secondary   circuit   for 
disc  type  of  rectifier. 


X-RAY  PHYSICS 


67 


Electro  Magnet  and  Solenoid. — Surrounding  a  wire 
while  it  is  carrying  an  electric  current  there  is  always  a 
magnetic  field  which  will  deflect  a  compass  needle  placed 
near  it  into  a  position  as  shown  in  Fig.  28.  If  now  the 
wire  be  wound  into  a  coil  the  magnetic  action  formerly 
distributed  along  the  length  of  the  wire  is  concentrated  in 
the  center  of  the  coil,  and  if  a  piece  of  iron  be  inserted  as 
a  core  the  intensity  of  the  field  will  be  still  further  in» 
creased  since  the  iron  is  much  more  permeable  to  magne- 

=  : 


-^^' 


<:::r> 


'U  U   U  U 


('rr. 


< — ". 


B 


<^V-4 


Fig.  28.  Eelation  between  an  electric  current  and  its  resulting 
magnetic  field,  (a)  Cross  section  of  conductor  with  compass  needle 
in  field,  (b)  Straight  portion  of  a  conductor  showing  current  and 
field,  (c)  Magnet  coil  with  iron  core.  Greater  strength  than  the 
same  coil  without  iron  core. 

tism  than  air.  The  coil  is  a  magnet  only  while  current  is 
actually  flowing  and  its  magnetic  strength  is  greater  the 
more  turns  of  wire  and  the  greater  the  current,  and  de- 
pends also  on  the  dimensions  and  quality  of  the  iron  core 
and  the  design  of  the  magnet  as  a  whole.  If  the  core  is 
fixed  and  the  magnetic  action  attracts  an  iron  armature, 
as  in  some  remote  control  switches,  it  is  called  simply  an 
electro-magnet,  whereas  if  the  winding  is  hollow  and  by 
its  magnetism  sucks  an  iron  plunger  into  the  coil,  as  in 
the  throttle  control  of  the  portable  unit  engine  and  cer- 
tain remote  control  switches,  it  is  called  a  solenoid.  An 


68  U.  S.  ARMY  X-RAY  MANUAL 

electro  magnetic  winding  should  never  be  connected  on  a 
voltage  for  which  it  was  not  designed,  and  a  winding  made 
for  a.c.  or  d.c.  must  never  be  connected  to  the  other  type 
of  current  supply,  as  is  explained  in  the  next  section. 

Choke  Coil. — If  an  alternating  current  be  applied  to  an 
electro  magnet  there  will  be  a  choking  effect  due  to  the 
slow  magnetizing  of  the  core  and  the  rapid  alternation 
of  the  current.  Less  current  will  flow  than  if  a  corre- 
sponding voltage  of  direct  current  be  applied,  and  the  dif- 
ference will  depend  on  the  properties  of  the  magnet  and 
the  frequency  of  alternation.  Never  expect  a  magnet  de- 
signed for  d.c.  to  operate  satisfactorily  on  a.c,  for  it  will 
not  let  pass  sufficient  current;  and  never  connect  an  a.-c. 
winding  to  d.-c.  lines,  since  so  much  current  will  flow  as 
to  most  likely  burn  out  the  coil  immediately. 

The  choke  coil  is  quite  generally  used  instead  of  a 
rheostat  as  a  means  of  control  for  the  Coolidge  filament 
transformer.  Variation  is  secured  by  moving  a  piece  of  iron 
in  or  out  of  the  field,  the  more  iron  in  the  field  the  more 
choking  effect  and  the  dimmer  the  filament,  and  the  less 
iron  the  brighter  the  filament.  Gradation  of  control  is  com- 
plete and  there  are  no  sliding  contacts  to  cause  trouble. 

Protection  against  Surge. — The  insulation  of  the  appa- 
ratus in  the  primary  circuit  is  sufficient  for  220  volts,  but 
not  for  high  tension.  If  a  sudden  impulse  or  surge  of  elec- 
tricity is  set  up  in  the  primary  circuit,  due  to  a  ground 
or  short  circuit  of  the  secondary,  or  a  spark  back  to  the 
primary,  the  voltage  in  the  circuit  may  amount  to  many 
times  what  it  normally  is. 

Most  of  the  apparatus  in  the  primary  circuit  is  induc- 
tively wound  (electromagnetic  coils  with  an  iron  core) 
and  offers  so  much  objection  to  the  passage  of  a  sudden 
surge  that  the  path  of  least  resistance  may  be  through 
the  insulation  of  the  coils  rather  than  through  the  com- 


X-RAY  PHYSICS  69 

plete  winding.  When  the  insulation  is  punctured  by  the 
momentary  pulse  of  high  tension  and  a  spark  established, 
the  low  voltage  is  able  to  maintain  this  spark  and  build 
up  a  heavy  arc,  resulting  in  a  burnout. 

Protection  against  surges  in  the  primary  can  be  secured 
by  connecting  in  shunt  with  the  main  transformer  and 
motor  a  protective  resistance,  as  shown  in  Fig.  13.  This 
resistance  is  so  high  that  it  normally  lets  pass  an  insig- 
nificant amount  of  current,  but  in  case  of  a  surge  the 
current  will  go  through  the  resistance  rather  than  break 
down  the  insulation,  and  the  apparatus  is  protected. 

The  protective  resistance  may  be  in  the  form  of  a  car- 
bon rod,  an  open  winding  of  fine  resistance  wire,  a  resist- 
ance wire  baked  into  an  enameled  porcelain  shell,  or 
simplest  of  all,  an  ordinary  incandescent  lamp.  If  the  more 
elaborate  devices  become  broken  and  cannot  be  replaced,  a 
lamp  should  be  substituted  rather  than  leave  the  equip- 
ment unprotected.  If  the  lamps  at  hand  are  not  of  suf- 
ficient voltage,  they  can  be  connected  in  series ;  two  110-volt 
bulbs  in  series  are  equivalent  to  a  220-volt  bulb. 

Remote  Control  Switch. — Machines  are  frequently 
equipped  with  remote  control  switches  or  contactors  which 
serve  to  make  and  break  the  heavy  primary  currents  and  to 
permit  the  use  of  a  small,  convenient  operating  switch.  The 
operating  push  button  or  other  device  makes  and  breaks  a 
small  current  in  an  auxiliary  circuit,  which  is  sufficient  only 
to  operate  the  magnetic  switch.  When  the  auxiliary  cir- 
cuit is  closed,  current  passes  through  the  magnet  of  the 
remote  control  switch  and  attracts  an  iron  armature,  there- 
by making  contact  and  closing  the  main  primary  circuit. 
When  the  auxiliary  circuit  is  opened  the  magnet  ceases  to 
attract  the  armature  and  a  spring  or  gravity  opens  the 
contacts  in  the  main  primary. 

The  timing  elements  of  most  timers  are  delicate  devices 


70  U.  S.  ARMY  X-RAY  MANUAL 

and  not  able  to  make  and  break  the  heavy  main  primary 
current.  They  should  be  connected  always  in  the  auxil- 
iary circuit  of  a  remote  control  switch,  where  the  current 
is  light  and  will  not  cause  damage,  and  they  should  never 
be  inserted  directly  in  the  main  primary  circuit. 

Line  Wiring. — The  line  for  x-ray  installations  should 
receive  more  careful  attention  than  has  usually  been  given 
to  such  important  work. 

The  primary  or  low  tension  wiring  should  contain  enough 
copper  to  insure  that  there  will  be  no  considerable  voltage 
drop  on  the  line  even  when  the  heaviest  work  is  done.  If  a 
line  from  a  supply  transformer  or  a  generator  has  a  resist- 
ance of  say  .3  ohms,  and  one  draws  50  amperes,  a  loss  of 
.3  X  50  =  15  volts  would  result.  If  the  original  voltage 
was  100,  the  total  available  at  the  x-ray  transformer  would 
be  85  volts.  On  220  volt  operation  this  is  not  so  serious, 
but  more  reliable  operation  will  be  attained  if  the  wire  is 
such  that  at  the  highest  primary  current  the  line  drop  does 
not  exceed  3  per  cent. 

When  a.-c.  lines  are  used,  the  transformer  from  which 
power  is  drawn  should  be  of  ample  capacity,  and  on  d.c. 
the  generator  should  have  a  capacity  exceeding  any  esti- 
mated demand.  Connecting  a  10  kw.  x-ray  transformer  to 
a  5  kw.  line  transformer  is  poor  business.  Fuses  or  circuit 
breakers  should  be  conveniently  placed,  and  all  care  should 
be  exercised  to  avoid  short  circuiting  or  grounding  the  lines. 

The  following  table  shows  the  loss  in  voltage  of  a 
primary  line  for  50  and  100  amperes  low  tension  current, 
on  the  assumption  of  a  run  of  100  feet  between  an  x-ray 
transformer  and  the  power  transformer,  giving  200  feet  of 
line.  The  terminal  voltage  to  be  taken  by  primary  and  con- 
trol is  the  difference  between  the  line  voltage  and  the  loss. 
Thus,  a  machine  drawing  100  amperes  for  a  short  exposure 
on  a  220  volt  circuit,  using  No.  10  wire,  will  have  220  — 


X-RAY  PHYSICS  71 

19.9,  or  about  200  volts  available.  On  110  volt  operation, 
110  —  19.9  =  90  volts,  making  a  very  decided  percentage 
drop.  For  this  reason,  machines  using  a  large  primary  cur- 
rent are  unsuited  for  110  volt  operation  if  rapid  work  is 
required. 

Volts  lost  Volts  lost 

200  ft.  50  Amp.      200  ft.  100  Amp. 
,778  1.5 

.98  1.96 

1.24  2.4 

1.56  3.1 

1.97  3.9 

2.48  4.9 

3.13  6.2 

3.94  7.8 

4.97  9.9 

6.27  12.5 

7.91  15.8 

9.97  19.9 

To  compute  the  size  of  wire  needed,  one  must  know:  (a) 
the  maximum  primary  current  in  the  x-ray  transformer; 
(b)  the  distance  from  the  supply  transformer  (or  genera- 
tor)  to  the  x-ray  transformer. 

The  loss  in  voltage  due  to  line  resistance  is  given  by 
the  product  of  current  in  amperes  hy  resistance  in  ohms 
of  line  wire  per  foot,  hy  length  of  supply  wires  in  feet. 
Thus,  on  a  220  volt  line,  if  a  drop  of  6  volts  is  permis- 
sible, the  line  being  200  feet  long  and  the  maximum 
current  60  amperes,  then 

60  X  200  X  Resistance  per  foot  =  6  volts 

6 

Resistance  per  foot  == =  .0005  ohms. 

60  X  200 


Ohms 

No. 

per  ft. 

00 

.0000778 

0 

.000098 

1 

.000124 

2 

.000156 

3 

.000197 

4 

.000248 

5 

.000313 

6 

.000394 

7 

.000497 

8 

.000627 

9 

.000791 

10 

.000997 

72  U.  S.  ARMY  X-RAY  MANUAL 

The  smallest  permissible  wire  then  is  "No.  7."  Better 
use  a  wire  considerably  larger  to  insure  the  best  opera- 
tion. 

High  Tension  Wiring. — In  the  use  of  high  power  ma- 
chines, much  greater  care  should  be  taken  in  high  tension 
construction  than  is  generally  the  case.  Three  points  should 
be  carefully  considered.  These  are:  First,  safety  of  the 
patient  and  operator;  second,  prevention  of  loss  by  leak- 
age ;  third,  avoidance  of  puncture  of  tubes. 

While  one  might  get  a  very  unpleasant  jolt  from  an 
induction  coil,  yet  danger  to  life  is  slight  as  compared 
with  transformers  of  like  voltage.  In  general,  a  main- 
tamed  voltage  of  500  through  vital  portions  of  the  body 
is  dangerous  if  a  current  of  100  ma.  or  more  can  be  de- 
livered. A  static  machine,  an  induction  coil,  or  a  con- 
denser may  give  a  high  initial  voltage  with  a  brief  rush 
of  current  upon  contact  or  grounding;  this  is  disagreeable 
but  usually  harmless.  In  a  power  transformer  which 
maintains  voltage,  the  current  continues,  with  possible 
fatal  results.  In  most,  if  not  all,  installations  the  middle 
of  the  secondary  coil  of  the  transformer  is  connected  to 
'the  iron  case  or  to  the  "earth";  the  earth  is  such  a  large 
reservoir  that  its  electrical  condition  may  be  regarded 
as  constant.  The  "ground"  need  not,  and  in  fact  should 
not,  be  completed  by  an  actual  metallic  connection  of 
transformer  case  to  a  water  or  gas  pipe.  Thus,  when 
working  at  60  kv.  between  the  tube  terminals,  the  volt- 
age between  the  +  line  and  the  earth  is  +  30  kv.,  and 
between  the  —  line  to  earth  —  30  kv. 

This  divides  the  insulation  strain  on  the  transformer 
and  reduces  danger  of  sparking  to  the  stand.  If  one  ter- 
minal of  the  transformer  were  grounded,  the  full  voltage 
would  tend  to  pass  current  from  the  other  line  to  any- 
thing connected  to  the  earth.    Thus,  there  would  "be  a  ten- 


X-RAY  PHYSICS 


73 


inch  spark  length  to  stand,  floor,  water,  and  gas  pipes,  etc. 
When  treating  at  a  ten-inch  gap  the  strain  is  then  double 
that  in  the  other  connection,  but  the  line  to  the  grounded 
side  of  the  transformer  is  safe  to  touch.  When  using  metal 
stands,  tables,  and  protecting  screens  with  the  metal  screens 
between  the  tube  and  the  patient,  they  should  be  well 
grounded.    The  patient  is  then  free  from  induced  ' '  static ' ' 


FiLfiMENT 
TRftNSFORMEH 


'Iron  pipe 
Two-by-four' 
Brass  tube      ( 


TO  TUB£ 


Micanite  sktve 
Tube- 


30- 


+W 


Section  at  "A" 


Fig.  29.  Arrangement  for  constant  resistance  between  filament 
transformer  and  Coolidge  filament.  Wire  may  be  used  instead  of 
brass  tube  in  the  same  way. 


and  from  any  discharge  that  may  occur  between  the  parts 
of  the  outfit.  When  the  patient  is  between  the  tube  and  the 
grounded  metal,  there  is  always  more  danger  to  the  patient, 
and  corresponding  care  must  be  used. 

Aside  from  the  difficulty  of  preventing  spark  discharges 
and  arcs,  it  is  of  great  importance  to  prevent  leakage  be- 
tween all  parts  having  a  high  potential  difference.  This 
leakage  is  due  to  high  electric  stress,  rendering  the  air 
conducting  and  giving  rise  to  ''corona."  Also,  many  good 
insulators  when  clean  and  dry  become  conducting  when 


74 


U.  S.  ARMY  X-RAY  MANUAL 


dusty  and  moist.    High  tension  wires  mounted  on  ordinary- 
wood  or  on  glass  may  be  expected  to  leak  badly. 

Surface  leakage  is  less  on  hard  rubber  and  micanite 
than  on  glass.  Wiping  insulating  surfaces  with  a  cloth 
slightly  moistened  with  kerosene  will  often  greatly  reduce 
leakage  over  the  surface. 

Corona  loss  is  decreased  by  reducing  the  electric  stress 
between  the  conductor  and  the  surrounding  air.     This  is 

accomplished  by  avoid- 
ing points,  sharp  edges, 
and  close  proximity  of 
conductors  of  high  po- 
tential difference.  High 
potential  overhead  lines 
should  be  from  24  to  30 
or  more  inches  apart. 
All  sharp  points  and 
corners  should  be  avoid- 
ed and  small  wires,  es- 
pecially if  cloth  insu- 
lated, should  not  be 
used.  Gutta  percha  cov- 
ered wire  without  braid- 
ed covering  is  useful  where  a  flexible  conductor  is  needed. 
For  rigid  wiring  and  overhead  lines,  metal  tubing  not  less 
than  half  inch  external  diameter  should  be  used.  This 
may  be  mounted  by  insulating  rods  attached  to  the  ceiling, 
or  as  shown  in  Fig.  29. 

The  same  design  can  be  easily  adapted  to  inter-con- 
necting rooms  by  mounting  the  tubing  in  the  center  of 
a  large  micanite  or  porcelain  tube  and  filling  the  space 
with  a  good  insulating  wax.  The  insulating  tube  should 
be  extended  6  to  8  inches  from  the  wall.  The  rings 
for  tube  connection  may  carry  reels  if  desired. 


"Fig.  30.  The  path  of  negative 
charge  from  line  through  spark  gap, 
tube  and  milliammeter. 


X-RAY  PHYSICS  75 

While  line  leakage  of  moderate  amount  may  be  toler- 
ated in  fluoroscopic  or  radiographic  work,  it  may  be  of 
great  importance  in  treatment.  A  milliammeter  measures 
not  alone  the  tube  current  but  all  leakage  beyond  the  in- 
strument itself.  Corona  between  wires,  spark  gap  corona 
and  surface  leakage  together  may  give  an  error  of  two 
or  three  hundred  per  cent.  We  may  avoid  this  (1)  by 
proper  design,  (2)  by  always  connecting  the  milliammeter 
beyond  the  spark  gap  as  shown  in  Fig.  30,  (3)  AYhere  any 
doubt  arises  check  by  testing  with  a  second  milliammeter 
connected  directly  to  the  tube. 

Tracing  Circuits. — The  modern  transformer  x-ray  ma- 
chine is  rarely  characterized  by  simplicity  of  wiring  or 
accessibility  of  connections.  In  case  of  trouble,  or  where 
one  must  connect  or  set  up  the  machine  without  expert 
aid,  it  is  well  to  learn  to  trace  the  circuits  and  to  test  out 
for  breaks,  etc. 

While  to  one  unaccustomed  to  do  this,  it  seems  very 
difficult,  a  few  suggestions  may  help.  There  are  only  two 
main  current  paths  from  one  supply  line  through  the  ap- 
paratus to  the  other  line — the  motor  circuit  and  the  trans- 
former circuit.  In  tracing  either  circuit,  follow  a  com- 
plete metallic  path  from  one  supply  line  through  the  motor 
or  transformer  back  to  the  other  supply  line.  Where  paths 
divide,  they  must  come  together  again  further  on,  and  one 
must  avoid  simply  chasing  around  some  loop.  The  main 
circuit  in  outline  on  all  resistance  controlled  machines  is 
shown  in  Fig.  31. 

Where  no  attempt  to  bring  the  motor  contact  into  cor- 
rect phase  is  made,  a  reversing  switch  is  provided,  Fig.  32, 
which  changes  polarity  of  transformer  without  disturbing 
the  motor  circuit.  There  may  be  a  special  switch  to  be 
operated  by  a  small  current  through  a  magnet.  Fig.  33. 
A  timer  connection  may  be  added,  as  in  Fig.  34.    Several 


76 


F     M 


U.  S.  AEMY  X-RAY  MANUAL 


Rh. 


Fig.  31.     Simple  primary  circuit,  rheostat  control. 


F     M 


Pol  "^^ 


Fig.  32.     Addition  of  reversing  switch  (polarity  changer). 


F    M 


Pol     \\ F[^^ 


0 

Fig.  33.     Magnetic  control- switch  added. 


-J 

Fig.  34.     Time  switch  and  foot  switch  added. 


X-RAY  PHYSICS 


77 


Fig.  35.    Multiple  taps   (''Inductance  taps")   added. 


Fig.   36.    Autotransformer  instead   of  multiple  primary  taps. 


A.  Autotransformer. 

C.  Coolidge   filament  transformer 

F.  Fuses. 

F.S.     Foot  Switch. 

F.S.S.S.  Foot  switch  safety  switch. 

G.  Ground  to  case  of  transformer. 
I.  Inductance  taps. 

K.V.    Kilovolt  meter. 
M.  Main  switch. 
Mot.    Motor. 


O.  Operating  switch. 
Pol.  Polarity  changer. 
Pol.I.    Polarity  indicator. 
Pr.  Primary  of  transformer. 
Prot.    Protective  resistance. 
R.  Remote  control  contactor. 
Eeg.    Filament  regulator. 
Ees.    Eesistance. 
Rh.  Rheostat. 
T.  Timer, 


78  U.  S.  ARMY  X-RAY  MANUAL 

taps  (inductances)  may  be  brought  out  from  the  primary- 
winding,  Fig.  35.  There  may  be  a  polarity  indicator  to 
show  the  way  to  place  the  reversing  switch  for  a  given 
tube  connection.  An  autotransformer  may  be  used  as 
the  control  device,  Fig.  36.  The  fundamental  wiring 
scheme  of  all  base  hospital  machines  likely  to  be  used  is 
shown  in  Fig.  37.  There  are  a  considerable  number  of  dif- 
ferences between  the  various  machines  but  they  all  con- 
form more  or  less  to  the  same  general  scheme.  Different 
models  put  out  by  the  same  manufacturer  may  be  no  more 
alike  than  the  different  makes.  Whatever  machine  be 
used,  to  become  familiar  with  the  wiring  will  help  to  quickly 
overcome  difficulties  when  they  arise. 

Locating  Trouble. — Troubles  in  x-ray  apparatus  may  be 
divided  into  two  groups:     (a)  mechanical;  (b)  electrical. 

Under  mechanical,  we  may  have  worn  bearings,  worn 
or  broken  brushes,  slip  of  rectifier  on  shaft;  warping  of 
wood,  thus  throwing  shaft  out  of  alignment.  Care  in 
oiling  and  keeping  apparatus  clean  and  dry  will  prevent 
most  of  these. 

Under  electrical  troubles  we  have:  (a)  Improper  con- 
nections; (b)  break  in  conducting  line;  (c)  loose  connec- 
tions;  (d)   failure  of  insulation. 

To  avoid  (a)  all  wires  removed  from  their  connections 
should  be  labeled  as  well  as  the  binding  posts,  etc.,  from 
which  they  were  disconnected.  Serious  damage  may  be 
done  if  one  attempts  to  operate  with  improper  connections. 

To  find  breaks,  close  switches  and  use  test  lamps,  as 
directed  in  the  following  pages.  When  the  lamp  lights 
on  connecting  two  points  between  which  the  resistance 
should  be  low,  there  must  be  a  poor  connection  or  a  break. 

Loose  contacts  are  likely  to  cause  irregular  or  intermit- 
tent action.     Failure  of  insulation  may  cause  current  to 


X-RAY  PHYSICS 


79 


80  U.  S.  ARMY  X-RAY  MANUAL 

pass  between  two  wires  without  going  through  the  proper 
path. 

If  the  fuse  in  any  part  of  the  circuit  blows  when  only 
moderate  power  is  used,  open  all  switches  and  look  for 
a  short  circuit;  and  if  none  is  found  insert  a  new  fuse 
and  test  out  on  low  power  before  attempting  to  continue 
work.  Beware  of  the  high  tension  line  and  terminals 
when  hunting  trouble  on  the  primary  or  motor  circuit. 


6 

Fig.  38.     Use  of  a  lamp  in  trouble  hunting. 

Primary  Circuit, — ^When  a  machine  which  has  been 
operating  fails  to  work,  there  must  be  trouble  in  either 
the  supply  or  some  part  of  the  circuit  insulation  or  wiring. 
The  low  tension  side  may  be  easiest  tested  by  using  an 
ordinary  incandescent  lamp  of  suitable  voltage.  Start  back 
of  the  fuses  on  the  main  line,  having  motor  and  transformer 
switches  open.    Fig.  38. 

Touch  lamp  terminal  wires  (bared  ends)  to  bare  wire 
at  1  and  2.  If  the  line  is  ''alive,''  a  220  volt  lamp  will 
light  up  to  half  brightness.  Do  the  same  for  2  and  3. 
Connect  1  to  5,  and  if  lamp  fails  to  light,  fuse  B  is  burned 
out.  Or,  if  switches  are  closed  and  the  lamp  lights  when 
connected  to  the  opposite  ends  of  a  fuse,  as  2  to  5,  the 


X-RAY  PHYSICS  81 

fuse  must  be  burned  out.  Try  2  to  4  and  2  to  6 ;  if  all 
these  connections  give  equal  brightness  to  the  filament, 
the  trouble  must  be  further  along. 

Close  motor  starting  switch,  and  if  motor  does  not  start 
connect  lamp  across  motor  fuses  one  at  a  time.  If  a  fuse 
is  intact,  it  has  so  low  a  resistance  that  current  will  not 
pass  through  the  lamp ;  if  broken,  the  full  line  voltage  ap- 
pears at  the  break,  and  the  lamp  will  light. 

Finally,  connect  across  the  motor  terminals,  and  if  the 
lamp  lights  fully  the  trouble  is  inside  the  motor. 

Follow  the  same  general  procedure  in  testing  the  trans- 
former circuit,  but  use  great  care  to  keep  away  from 
the  high  tension  terminals;  also,  be  sure  to  set  rheostat 
at  lowest  power. 

If  the  lamp  lights  across  the  low  tension  terminals  and 
no  spark  can  be  driven  across  a  short  gap  between  the 
secondary  terminals,  the  trouble  is  inside  the  transformer 
and  the  chance  of  its  repair  by  an  operator  is  slight.  If 
a  break  is  near  the  terminals,  it  may  sometimes  be  located 
and  repaired ;  otherwise  it  must  be  sent  to  a  manufacturer. 

Secondary  Circuit. — Outside  of  a  break  in  the  second- 
ary coil  or  an  arc  to  the  case,  the  most  common  trouble  in 
the  secondary  line  is  a  complete  or  partial  short  circuit. 
This  may  occur  in  various  ways: 

1.  In  a  cross  arm  machine,  the  insulation  may  break 
down  between  the  cross  conductor  and  the  rectifier  shaft. 

2.  In  a  disc  machine,  the  disc  may  be  dirty  or  car- 
bonized, ''shorting"  around  the  periphery  or  to  the  motor 
shaft. 

3.  A  high  tension  line  may  be  in  contact  with  the  tube 
stand,  a  wall  containing  metal  lath,  the  floor,  etc. 

The  latter  may,  of  course,  be  remedied  at  once  by  the 
operator. 


82  U.  S.  ARMY  X-RAY  MANUAL 

In  case  of  rectifier  trouble,  a  Coolidge  tube  may  be  run 
directly  on  the  transformer,  provided  low  spark  gap  and 
current  is  used  so  that  the  target  does  not  get  hot.  For 
fluoroscopic  work  there  is  no  trouble  in  doing  this,  but 
for  radiography  time  must  be  allowed  between  exposures 
for  the  target  to  cool. 

Care  of  Tubes. — All  tubes  are  fragile  and  may  easily  be 
damaged  by  fracture.  A  warm  tube  must  not  be  placed  on 
a  cold  support.  Keep  tubes  free  from  dust  and  moisture. 
Do   not   allow   either  high  tension  wire  to   come   within 

Reducer 
Raiser         ,. 


Fig.  39.     Diagram   showing  softening  and  raising  connections  on 
Snook  hydrogen  tube. 

five  or  six  inches  of  the  glass  bulb.  Always  heat  the  fila- 
ment of  the  Coolidge  tube  before  attempting  to  pass  cur- 
rent through  it.  Preserve  cases  or  frames  in  which  tubes 
are  received  for  the  return  of  punctured  tubes  or  those 
requiring  repumping.  Use  great  care  in  softening  gas 
tubes.  Never  soften  a  gas-containing  tube  with  rheostat 
set  for  heavy  radiography ;  use  low  power.  If  a  tube  is  too 
soft,  the  rays  emitted  will  not  pass  through  the  flesh.  Bet- 
ter take  more  time  and  soften  stepwise,  testing  after  each 
short  passage  of  current  through  the  softener. 

To  soften  the  Snook  hydrogen  tube,  pass  through  the 
reducer  about  15  ma.  five  or  ten  seconds  at  a  time.     Re- 


X-RAY  PHYSICS  83 

peat  if  necessary.  Do  not  use  more  current ;  use  more  time. 
Always  maintain  polarity,  as  shown  in  Fig.  39. 
To  harden  the  tube,  pass  through  the  raiser  about  25  ma. 
(never  more  than  30  ma.)  twenty  seconds  at  a  time.  If 
the  tube  is  excessively  soft,  disconnect  spiral  temporarily 
from  +  terminal  of  raiser.  Connect  anode  wire  to  + 
terminal  of  raiser  and  cathode  to  —  terminal  of  raiser. 
Run  three  minutes  with  22  to  25  ma.  Repeat  if  neces- 
sary. Replace  spiral.  Regulate  tube  before  making  ex- 
posure. It  should  test  out  at  2-inch  gap  and  about  5  ma. 
The  tube  tends  to  harden  a  trifle  during  the  first  exposure 
when  the  tube  is  cold.  To  compensate,  introduce  a  little 
more  gas.  Operate  at  40  ma.  for  a  medium  focus  tube. 
It  will  give  much  more  service  than  at  45  to  50  ma.  A 
sharp  focus  should  be  limited  to  20  ma.  and  the  time  of 
exposure  doubled.  Use  a  broad  focus  tube  for  extremely 
fast  exposures  in  making  stomach  and  intestinal  plates. 

When  a  tube  is  in  operation,  the  heat  developed  at  the 
target  is  measured  by  the  current  x  voltage.  If  this 
heat  is  produced  at  such  a  rate  that  it  cannot  be  dissi- 
pated by  conduction  and  radiation,  the  metal  at  the  focal 
spot  may  be  vaporized  or  melted  and  the  tube  ruined  very 
quickly. 

It  is  rarely  necessary  to  do  so-called  flash  or  instanta- 
neous work,  and  it  can  only  be  done  at  high  tube  cost.  Prop- 
erly used,  a  tube  is  capable  of  a  large  amount  of  work. 

Do  not  use  intermittent  excitation  during  an  exposure. 
In  heavy  work,  if  60  ma.  for  four  seconds  overheats  the 
tube  at  the  gap  needed,  many  operators  close  the  switch  for 
four  separate  seconds  with  three  intervals  of  a  second  or 
more.  The  patient  must  remain  at  rest  for  seven  seconds. 
The  same  exposure  may  be  secured  with  40  ma.  continu- 
ously delivered  for  six  seconds.  In  the  latter  case  the 
danger  of  pitting  or  cracking  the  target  is  less  and  the 


84  U.  S.  ARMY  X-RAY  MANUAL 

part  need  be  held  immobile  for  less  time.  This  intermit- 
tent method  has  been  suggested  to  overcome  the  tendency 
for  voltage  drop  on  heating  gas  tubes  while  in  operation, 
but  the  allowable  interval  is  too  short  to  do  much  good. 

Care  of  Motors. — 1.  All  motors  need  oil  at  periods  de- 
pending on  the  amount  of  use.  Failure  to  oil  may  cause 
the  bearings  to  wear  enough  to  allow  the  armature  to  rub 
on  the  field  supports  and  ruin  the  motor.  Follow  the 
maker's  instructions,  if  any  are  given.  Do  not  use  too 
light  an  oil.  An  oil  like  3  in  1  is  good  for  sewing  ma- 
chines, but  must  not  be  used  on  power  motors.  Use  real 
machine  oil. 

2.  Most,  if  not  all,  motors  used  on  x-ray  machines  have 
either  slip  rings  or  commutators,  or  both.  Bearing  on  these 
are  carbon  or  other  conducting  brushes.  As  the  tension  is 
low,  these  must  have  a  good,  even  contact.  Springs  are 
provided  to  secure  this,  and  if  these  break  or  get  out 
of  adjustment  there  will  be  either  intermittent  contact  or 
none.  The  motor  then  either  fails  to  start  or  it  sparks  at 
these  bad  contact  points  and  corrodes  the  metal  rings  or 
commutator  bars.  If  only  slightly  injured,  they  may  be 
smoothed  down  by  00  sandpaper  (not  emery  cloth),  lubri- 
cated slightly  with  paraffin  or  light  oil  and  rubbed  off  with 
a  clean  cloth.  New  brushes  should  be  inserted  before  any 
serious  trouble  occurs.  Be  sure  and  put  them  in  right, 
noting  carefully  how  the  old  ones  were  placed. 

3.  Many  motors  have  two  sets  of  connections,  one 
for  starting,  the  other  for  running.  Usually  a  double  throw 
switch  is  used  and  marked  for  the  purpose.  Don't  close 
on  the  running  side  and  wait  for  something  to  happen. 
Don 't  throw  over  too  quickly.  Don 't  leave  switch  on  start- 
ing position. 

4.  Keep  motor  clean  and  in  as  dry  a  place  as  circum- 
stances permit. 


X-RAY  PHYSICS  85 

5.  If  the  motor  fails  to  start,  open  the  starting  switch 
and  test  the  fuse  on  the  motor  circuit;  also  be  sure  the 
line  is  ''alive."  If  power  is  on  and  the  fuse  is  intact,  go 
carefully  over  the  wiring  to  the  motor,  examine  brushes, 
look  at  all  external  wires,  and  if  no  break  is  found  it  is 
fairly  probable  that  some  internal  trouble  has  developed 
requiring  technical  motor  knowledge  for  repair. 

6.  Be  very  sure  not  to  connect  a  motor  on  a  line  for 
which  it  was  not  designed, — as  an  a.-c.  motor  on  a  d.-c. 
line ;  or  a  220  volt  motor  on  a  110  volt  line,  or  the  reverse ; 
or  an  a.-c.  motor  designed  for  60  cycles  on  a  40  cycle 
line,  etc. 

7.  If  an  a.-c.  motor  fails  to  run  at  the  right  speed,  do 
no  try  to  operate  tubes  with  it. 

8.  It  is  well  to  have  the  field  and  the  armature  of  an 
x-ray  motor  protected  from  small  sparks  due  to  transient 
surges.  Ordinary  incandescent  lamps  in  shunt  serve  very 
well  for  this  purpose.  Most  machines  have  such  protection, 
using  either  lamps,  or  special  high  resistances,  or  con- 
densers. 

Care  of  Transformers. — The  attention  of  every  roent- 
genologist should  be  called  to  the  danger  to  the  x-ray  trans- 
former arising  from  carelessness  in  operation.  There  are 
certain  things  which  should  never  be  done  even  though  they 
might  be  done  many  times  without  damage. 

1.  Never  operate  at  high  applied  voltage  when  the 
tube  is  taking  no  current,  or  on  an  open  circuit,  especially 
with  rheostat  control  on  high  buttons.  In  this  case  the 
effective  gap  measuring  the  strain  upon  the  insulation  may 
be  very  much  in  excess  of  what  is  needed  in  practice. 

2.  High  tension  wires  should  not  come  in  contact  with 
or  close  to  steam  or  gas  pipes,  electric  service  wires,  metal 
ceilings  or  walls,  metal  tube  stand,  or  the  x-ray  cabinet. 
Keep  them  away  from  things,  where  they  belong.    When 


86  U.  S.  ARMY  X-EAY  MANUAL 

a  discharge  occurs  from  one  high  tension  line  to  the  earth 
the  danger  to  the  insulation  of  the  transformer  may  be 
greater  than  in  the  case  of  a  discharge  between  the  two 
lines. 

3.  In  all  cases  when  starting  up  the  machine  test  out 
for  proper  operation  on  low  power  and  especially  be  care- 
ful not  to  attempt  operation  of  any  kind  of  tube  with 
rectified  current  of  wrong  polarity.  If,  on  moderate  fila- 
ment current  and  a  low  power  setting,  no  current  is  drawn 
through  a  Coolidge  tube,  reverse  the  polarity  and  again 
test.  After  a  machine  is  once  up  to  synchronism  it  will  very 
rarely  change  polarity  while  running,  but  it  may  do  so 
in  case  of  a  momentary  interruption  of  service  or  unsatis- 
factory line  conditions.  It  is  wise,  whenever  lights  operat- 
ing on  the  same  power  circuit  as  the  x-r^  apparatus  be- 
come dim  or  are  temporarily  extinguished,  to  throw  the 
machine  to  low  power  and  again  test  for  polarity. 

4.  Look  to  the  oil  level  about  every  two  months  and 
record  the  date  on  a  tag  attached  to  the  transformer.  If 
the  level  is  low,  add  more  oil  until  all  the  coils  are  properly 
covered.  Be  sure  to  use  transformer  oil  that  has  not  been 
open  and  exposed  to  dirt  and  moisture.  Wipe  oil  and 
dirt  oif  the  top  of  the  transformer  case. 

5.  Be  sure  that  the  transformer  is  adequately  pro- 
tected against  surges  by  a  suitable  type  of  protective  re- 
sistance. 

Care  of  Batteries. — The  only  type  of  battery  likely  to  be 
met  in  x-ray  practice  is  the  storage  battery.  This  is  some- 
times used  for  portable  coil  work,  and  quite  often  to  light 
the  Coolidge  filament.  Each  separate  cell  of  a  storage 
battery  adds  about  two  volts  to  the  4ine.  For  any  given 
voltage,  then,  half  as  many  cells  must  be  used  as  volts 
are  needed.  This  voltage  is  independent  of  the  size  of 
the   cells.     A   storage   cell  does  not   store  electricity;   it 


X-RAY  PHYSICS  87 

uses  electricity  to  cause  a  chemical  change  in  its  plates, 
and  when  it  is  discharged  this  chemical  change  is  reversed 
and  electric  current  flows  from  the  cell.  The  amount  of 
chemical  change  on  proper  charge  is  in  proportion  to  the 
charging  current  and  the  time  of  flow,  and  is  estimated 
in  ampere-hours. 

Thus,  a  10  ampere-hour  battery  will  deliver  ten  amperes 
for  one  hour,  1  ampere  for  ten  hours,  %  an  ampere  for 
twenty  hours,  etc.  Too  rapid  charge  or  discharge  should 
be  avoided  because  of  damaging  the  battery. 

The  storage  battery  consists  of  two  sets  of  plates,  each 
containing  a  salt  of  lead  held  in  some  sort  of  small  lead 
pockets,  the  whole  being  immersed  in  a  solution  of  sul- 
phuric acid.  In  a  single  cell,  all  the  positive  plates  are 
joined  together,  likewise  all  the  negative,  and  these  sets 
must  not  be  in  contact.  The  negative  of  one  cell  must 
be  joined  to  the  positive  of  an  adjacent  one,  leaving  one 
-f-  and  one  —  for  external  connection.  The  ampere- 
hour  capacity  depends  on  the  area  of  -|-  and  —  plates  per 
cell. 

The  following  are  the  main  points  to  be  kept  in  mind 
when  using  storage  batteries: 

1.  They  must  be  charged  on  direct  current. 

2.  The  charging  rate  given  by  the  maker  should  not 
be  exceeded. 

3.  The  discharge  rate  allowable  should  not  be  exceeded. 

4.  Loss  of  electrolyte  by  evaporation  must  be  replaced 
by  adding  distilled  water,  rain  water,  or  as  pure  water  as 
can  be  had. 

5.  Loss  of  electrolyte  by  accidental  spilling  must  be 
replaced  by  adding  an  acid  solution  of  the  proper  den- 
sity. 

6.  In  making  up  an  acid  solution,  never  pour  water  into 
the  acid,  but  pour  acid  slowly  into  the  water. 


88 


U.  S.  ARMY  X-RAY  MANUAL 


7.  Never  let  the  solution  get  so  low  as  to  leave  a  por- 
tion of  the  plates  bare. 

8.  Do  not  overcharge,  nor  discharge  after  the  voltage 
falls  below  1.8  volts  per  cell. 

9.  Do  not  let  the  battery  freeze. 

10.  Do  not  let  the  battery  stand  idle  for  long  periods. 
If  it  must  be  laid  up,  charge  it  fully  and  draw  off  the 
solution.  For  short  periods,  put  a  high  resistance  across 
its  terminals  and  let  it  slowly  discharge,  and  charge  it 
up  again  at  intervals. 


--»■-       + 


B 


B 


Fig.  40.     Storage  battery  charging:  BB — two  cells  in  series;   V — 
voltmeter:   A — ammeter. 


11.  If  overheated  by  too  high  current  passing  m  or  out, 
the  active  material  is  likely  to  crumble  and  fall  to  the 
bottom  of  the  cell  and  cause  a  short  circuit,  whereby  the 
battery  discharges  internally. 

12.  The  discharge  voltage  falls  quite  rapidly  after  a 
battery  is  first  charged,  then  more  slowly  until  nearly 
discharged,  then  rapidly.  "When  used  on  a  Coolidge  fila- 
ment, which  requires  about  four  amperes,  it  is  well  to  pass 
twelve  or  fifteen  amperes  through  a  suitable  resistance  for 
three  or  four  minutes  to  bring  the  voltage  down  to  the 
steady  state  the  first  time  it  is  used  after  charging. 


X-RAY  PHYSICS  89 

13.  A  small  voltmeter  is  very  useful  in  charging  a  bat- 
tery, and  a  suitable  resistance  to  bring  the  line  voltage  down 
to  that  required  in  charging  should  always  be  at  hand. 
Either  a  voltmeter  or  a  test  for  acid  density  may  be  used 
to  indicate  full  charge. 

14.  Do  not  fail  to  disconnect  the  charging  line  before 
using  on  a  Coolidge  tube. 

15.  Storage  cell  terminals  are  almost  sure  to  corrode; 
scrape  clean  when  connecting. 

The  charging  connections  are  shown  in  Fig.  40.  If 
the  battery  has  any  charge,  it  will  deflect  the  voltmeter 
in  the  same  direction  when  discharging  as  when  charg- 
ing. Connect  the  voltmeter  in  the  right  way  before  start- 
ing to  charge,  and  it  will  tell  you  whether  you  have  con- 
nected to  the  charging  line  correctly.  The  ammeter  may  be 
omitted  if  one  knows  that  the  charging  current  is  neither 
too  large  nor  too  small. 

Emergency  Provisions. — In  military  x-ray  work  it  is  of 
the  utmost  importance  that  apparatus  be  kept  going  at  all 
times  to  meet  the  demands  that  are  placed  upon  it.  The 
roentgenologist  must  keep  in  mind  the  human  lives  de- 
pendent on  him,  and  he  must  make  every  effort  to  repair, 
improvise,  or  do  without  whatever  piece  of  apparatus  may 
fail  in  the  rush  of  work.  There  may  be  loss  of  time  in 
securing  replacement  parts  or  repair  assistance,  and  during 
this  delay  the  plant  must  be  maintained  in  operation.  The 
following  are  some  suggestions  for  emergencies. 

Polarity  Indicator. — This  piece  of  apparatus  may  be 
classed  as  a  luxury,  and  in  case  repair  cannot  readily  be 
made  no  interruption  of  sarvice  is  warranted.  With  a  gas 
tube,  polarity  is  readily  shown  by  the  appearance  of  the 
tube.  Correct  polarity  results  in  a  uniform  color  and 
inverse  in  a  series  of  rings.  With  a  Coolidge  tube  the 
milliammeter  serves  as  a  guide,  for  no  current  will  flow 


90  U.  S.  ARMY  X-RAY  MANUAL 

through  the  tube  in  the  inverse  direction.  If  the  meter 
registers,  the  polarity  is  right.  Always  test  on  low  power 
to  avoid  puncturing  the  tube.  Spark  gap  may  be  used 
as  an  index  if  the  meter  also  has  failed,  since  on  the  same 
control  setting  the  gap  will  be  greater  when  the  tube 
is  not  taking  current  than  when  it  is. 

In  case  of  burnout  of  the  resistance,  sometimes  in- 
cluded in  the  polarity  indicator  circuit,  an  incandescent 
lamp  may  often  be  substituted.  Never  attempt  to  connect 
up  without  the  resistance. 

Milliammeter. — In  working  without  a  milliammeter  the 
appearance  of  a  Coolidge  tube  gives  no  idea  as  to  the 
amount  of  radiation  produced.  If  the  machine  is  on  a 
steady  power  line  the  transformer  chart  may  be  used  as 
an  accurate  means  of  obtaining  a  setting  of  the  machine. 
Suppose  a  5-inch  gap  and  40  ma.  is  desired,  refer  to  the 
chart  and  find  which  control  button  must  be  used.  Then, 
instead  of  using  the  chart  in  the  customary  way,  set  the 
gap  for  5  inches  and  vary  the  filament  temperature  until 
the  spark  is  barely  able  to  break  the  gap.  The  milliam- 
perage  will  now  be  right — 40  ma. 

The  appearance  of  a  gas  tube  is  somewhat  of  a  guide  to 
tube  current,  but  if  an  accurate  chart  has  been  made  of 
the  machine  it  is  safer  to  refer  to  that.  At  what  appears  to 
to  be  a  working  setting,  measure  the  spark  gap.  Then 
see  what  current  corresponds  to  this  gap  on  the  control 
button  used. 

In  working  under  uncertain  conditions,  he  sure  thai  the 
spark  gap  is  as  high  as  it  should  he.  A  difference  in  tube 
current  will  affect  only  the  quantity  of  radiation;  a  dif- 
ference in  voltage  not  only  changes  the  quantity  but  the 
penetration  as  well. 

Timer. — If  the  timer  fails,  exposures  may  be  made  ac- 
cording to  the  second  hand  of  a  watch  or  by  counting 


X-RAY  PHYSICS  91 

seconds.  *'One  thousand  one,  one  thousand  two,  one  thou- 
sand three,"  etc.,  is  a  convenient  method,  and  a  little  prac- 
tice will  enable  one  to  keep  close  pace  with  a  stop  watch. 

Remote  Control. — In  case  of  failure  of  the  remote  con- 
trol magnet  coil  or  another  device  in  its  circuit  the  custo- 
mary operating  switch  will  be  of  no  service.  It  is  pos- 
sible, in  some  instances,  to  wire  around  the  remote  control 
switch,  ,or  block  it  closed,  and  operate  from  an  auxiliary 
switch  in  the  main  circuit,  such  as  a  pole-changing  switch. 
Of  course,  care  must  be  taken  to  always  close  the  switch  the 
right  way,  otherwise  there  is  great  danger  of  tube  breakage 
and  sparking  to  the  patient  on  inverse  polarity.  Or,  in 
some  cases  it  would  be  more  convenient  to  operate  by  hold- 
ing the  remote  control  switch  closed  with  a  stick  during 
the  exposure. 

Protective  Resistance. — If  the  shunt  resistance  or  con- 
densers protecting  against  surges  become  broken  or  un- 
serviceable, do  not  leave  the  circuits  unprotected,  since  a 
more  vital  element  may  be  damaged.  An  incandescent 
lamp  of  proper  size  and  voltage  (usually  220  Y,  16  candle 
power,  carbon  filament)  connected  in  shunt  as  shown  in 
Fig.  13  is  very  good  protection. 

Motor  or  Rectifier. — In  case  of  breakage  of  the  rectifier 
or  burnout  of  the  synchronous  motor,  work  may  still  be 
done  by  working  on  low  power  and  letting  the  Coolidge 
tube  do  its  own  rectifying.  (If  the  rotary  converter  fails 
on  a  direct  current  installation  and  alternating  current  is 
not  available,  nothing  can  ordinarily  be  done.)  Set  the 
rectifier  in  position  so  there  will  be  a  minimum  of  spark- 
ing distance  to  the  collector  brushes,  or  wire  across  these 
gaps.  Leave  the  motor  switch  open,  or  in  case  it  must 
be  closed  to  get  current  through  the  main  primary  and 
filament  primary  circuits,  disconnect  the  lead  wires  to  the 
motor  and  tape  the  ends  to  prevent  short  circuit.     Then, 


92  U.  S.  ARMY  X-RAY  MANUAL 

starting  on  low  power,  set  the  tube  for  a  5-incli  working  gap 
and  5  ma.  All  Coolidge  tubes  will  operate  self-rectifying 
so  long  as  the  target  does  not  become  hot  enough  to  emit 
an  appreciable  number  of  electrons.  Do  not  work  at 
more  than  5  ma.  and  do  not  let  the  target  heat  to  redness, 
or  the  tube  will  no  longer  rectify,  and  will  very  soon  be 
ruined. 

Spark  gap  is  not  a  reliable  guide  to  working  voltage  in 
a  self-rectifying  tube,  since  the  inverse  voltage  is  higher 
than  the  working  voltage.  (See  page  37.)  The  excess 
over  working  voltage  depends  on  the  resistances  in  circuit 
and  the  type  of  control.  To  secure  a  setting  of  5-inch 
working  gap  and  5  ma.,  refer  to  the  chart  of  the  machine 
and  set  to  5  ma.  on  the  proper  control  button.  Check  by 
seeing  that  the  spark  gap  is  approximately  that  at  which 
the  chart  line  crosses  the  vertical  axis  of  the  chart.  Be 
sure  that  the  working  voltage  is  what  it  should  be  to  give 
rays  of  adequate  penetration.  Do  all  radiographic  work 
either  by  giving  increased  time  or  by  using  intensifying 
screens  and  exposing  as  with  the  bedside  unit. 

Autotrans former  or  Rheostat. — On  many  machines  hav- 
ing combined  control,  a  failure  of  one  of  these  elements 
would  merely  necessitate  leaving  it  out  of  circuit  and 
controlling  by  the  other.  Broken  wires  or  burned-out 
coils  in  a  rheostat  are  easily  wired  across,  but  a  failure 
in  an  autotransformer  is  a  much  more  difficult  proposi- 
tion. In  case  it  is  necessary  to  improvise  a  complete 
new  control,  this  may  be  done  by  building  a  water  rheo- 
stat. 

Fill  a  large  wooden  pail  with  water  and  drop  into  it  a 
lead  or  iron  plate  of  about  60  square  inches  area  with  wire 
attached,  for  an  electrode,  as  in  Fig.  41.  Suspend  securely, 
and  so  its  immersion  may  be  definitely  controlled,  a  smaller 


X-RAY  PHYSICS 


93 


snLT 

SOLUTION 


piece  of  metal  as  the  other  electrode.  Immerse  it  slightly 
to  correspond  to  the  lowest  power  setting  desired.  Test 
it  out,  and  add  ordinary  salt  slowly,  making  sure  that  it  is 
all  dissolved,  and  testing  at  intervals  until  the  desired 
low-power  setting  is  reached.  Pure  water  is  a  very  poor 
conductor  of  electricity,  and  the  addition  of  salt  lowers 
the  resistance  of  the  solution  to  the  desired  amount.  High- 
er powers  will  be  secured  by  immersing  the  upper  elec- 
trode deeper  in  the  so-     .. 

,     ^.  ,     ,  X     CONTROL  ELECT/rODE 

lution  and  lower  pow- 
ers by  withdraw- 
ing  it. 

It  may  be  noted  that 
in  case  of  failure  of 
both  rheostat  and  auto- 
transformer  on  220  volt 
machines,  as  a  general 
rule  we  may  secure  rea- 
sonable operation  by 
applying  110  volt  serv- 
ice directly  to  the  220 
volt  connections  on  the 

transformer.  Then  select,  when  using  the  Coolidge  tube, 
that  current  which  will  give  a  5-inch  gap  and  modify 
exposures  if  the  current  is  greater  or  less  than  that  usually 
employed. 

Fuses. — In  case  the  supply  of  plug  or  cartridge  fuses 
runs  out  never  wire  across  the  cut-out  block  with  copper 
wire.  Have  an  ample  supply  of  10  ampere  fuse  wire  on 
hand  and  include  the  proper  amount  of  this  in  the  cir- 
cuit. To  fuse  for  30  amperes  use  3  strands  in  parallel, 
for  50  amperes  use  5  strands,  and  so  on.  Fig.  42.  For  less 
than  ten  amperes  the  wire  may  be  whittled  down  to  smaller 
cross  section.     The  length  of  the  fuse  wire  does  not  alter 


Fig.  41. 
control  of 
former. 


LEffD  PLATE 


Emergency    rheostat    for 
primary    of    x-ray    trans- 


94 


U.  S.  ARMY  X-RAY  MANUAL 


the  current  at  which  it  will  blow,  nor  does  the  voltage 
of  the  line  on  which  it  is  used. 

The  above  suggestions  cover  most  of  the  cases  that  are 
likely  to  occur.  The  resourcefulness  of  the  roentgenologist 
is  relied  upon  to  cover  the  others  and  to  keep  his  plant 
in  operation  so  long  as  he  has  electric  power,  a  transformer, 
and  a  tube.  With  these  three  essentials  and  a  little  in- 
genuity he  should  be  expected  to  generate  x-rays  and  do 
creditable  work  in  an  emergency  rather  than  shut  down 
and  wait  for  assistance. 

Ordering  Supplies  and  Repairs. — Much  delay  and  incon- 


CP      GO 


10/^. 


m    m 


I 


20/9.       50/9.        40fi,        50ft. 


Fig.  42.     Method  of  using  10  ampere  fuse  wire  to  secure  capacity 
desired.    It  may  be  soldered  to  the  brass  ends  of  the  burned  out  fuses. 

venience  will  be  avoided  if  care  is  taken  to  state  explicitly 
just  what  is  wanted  and  the  exact  quantity.  The  work 
of  the  supply  depot  must  be  done  by  people  who  cannot 
be  familiar  with  every  minute  detail  of  x-ray  equipment, 
and  mind  readers  are  scarce. 

When  ordering  a  machine  specify: 

1.  Type  of  current,  a.c.  or  d.c. 

2.  The  frequency  of  cycles,  if  a.c. 

3.  The  voltage. 

4.  The  power  available  in  kw. 

5.  Gauge  and  length  of  wire  needed  to  connect  up. 

6.  If  d.c,  always  specify  a  rotary  converter  and  the 
d.-c.  voltage. 

7.  Be  sure  to  state  that  the  motor,  transformer  and 


X-RAY  PHYSICS  95 

Coolidg-e  filament  transformer  when  used  on  154  volts  or 
70  volts  a.c.  from  a  rotary  must  operate  properly. 

Thus — 220-volt-a.c.-60  cycle-10  kw — specifies  a  definite 
type  of  machine. 

In  ordering  repair  parts  state  the  name  of  the  apparatus, 
the  maker,  if  known,  and  either  give  a  drawing  or  such 
an  exact  description  or  name  as  to  identify  the  piece  re- 
quired. Sometimes  one  may  return  a  broken  or  defective 
part  as  a  complete  identification. 

In  case  of  supplies  be  sure  to  give  the  amount  and  any 
other  information  that  will  make  your  needs  clearly  un- 
derstood. Thus  an  order  for  ''an  x-ray  screen"  is  mean- 
ingless; one  for  a  ''10  x  10  inch  Patterson  fluoroscopic 
x-ray  screen,  mounted  with  lead  glass,"  is  definite. 

Never  fail  to  give  complete  address  to  which  goods  are 
to  be  forwarded. 

No  small  part  of  what  we  protest  against  as  *'red  tape" 
is  made  necessary  by  failure  of  individuals  to  convey  a 
clear  idea  of  what  they  desire. 

When  possible  confine  your  requests  to  those  articles 
specified  in  the  supply  tables. 

Induction  Coils. — It  sometimes  becomes  necessary  to 
work  for  a  time,  at  least,  with  an  induction  coil.  While 
not  often  used  in  this  country  one  must  be  prepared  to 
use  it  if  need  be  abroad. 

Coil  Characteristics. — ^A  good  induction  coil  should  be 
able  to  give  a  heavy  discharge  at  a  voltage  high  enough 
to  break  a  10-  or  12-inch  gap. 

Under  no  circumstances  must  a  coil  be  operated  at  high 
power  long  enough  to  heat  the  insulation,  as  the  insulat- 
ing power  is  mxuch  reduced  at  high  temperatures.  Each 
coil  has  its  own  characteristics  which  determine  its  best 
working  conditions.  These  characteristics  depend  on  the 
primary  and  secondary  resistances,   on  the  amount  and 


96  U.  S.  ARMY  X-RAY  MANUAL 

quality  of  iron  in  the  core,  on  the  number  of  turns  in 
the  coil,  and  on  the  mode  of  winding. 

The  most  undesirable  feature  in  coil  operation  for  x- 
ray  work  is  the  unavoidable  inverse  which  must  be  mini- 
mized in  the  use  of  the  ordinary  tube.  The  amount  of 
inverse  depends  on  the  coil,  the  interrupter  and  the  tube. 
A  coil  having  a  considerable  number  of  primary  turns 
and  but  little  ''magnetic  leakage"  gives  less  trouble  with 
inverse  than  other  types. 

The  direction  of  secondary  current  while  the  primary 
is  increasing  is  opposite  to  that  during  a  decrease  of 
primary  current.  Generally  it  is  possible  to  reduce  pri- 
mary current  at  a 
greater  rate  than  that 
at  which  it  can  be  built 
up.  Hence  the  ''break" 
voltage  is  usually  high- 
er than  that  at  "make." 

The   current   of  higher 

Fig.  43.    Valve  tube.  -,,  -  j?  i   •_  +i,« 

voltage  IS  useiui  m  the 

tube,  but  the  inverse  is  not  only  ineffective  for  ray  pro- 
duction but  is  a  source  of  positive  injury  to  the  ordinary 
tube.  If  the  make  current  could  be  caused  to  rise  slowly 
enough,  the  resulting  secondary  voltage  would  not  force 
current  through  the  tube.  In  practice  this  is  not  pos- 
sible, although  the  voltage  giving  "inverse"  may  be  very 
much  smaller  than  that  giving  "direct." 

Valve  Tubes. — In  order  to  reduce  "inverse"  as  far  as 
possible,  various  unsymmetrical  tubes.  Fig.  43,  have  been 
devised ;  these  offer  much  greater  resistance  to  discharge  in 
one  direction  than  the  other.  Such  valve  tubes  are  often 
supplemented  by  a  series  of  small  spark  gaps  which  are 
readily  broken  down  by  the  ' '  direct, ' '  but  not  by  the  lower 
voltage  "inverse."     These  devices  all  reduce  the  energy 


X-RAY  PHYSICS 


97 


available  for  x-ray  production.  Fig.  44  shows  a  tube 
designed  to  indicate  the  presence  of  inverse.  If  there  is 
no  inverse,  only  one  of  the  metal  terminals  at  the  gap 


^ 


A 


^»> 


Fig.  44.    Vacuum  tube  oscilloscope. 


will  glow.     If  both  glow  to  the  same  extent,  inverse  cur- 
rent is  present. 

Fig.  45  shows  the  wiring  diagram  for  a  coil  with  mer- 


INTEFRUPTEB 

Fig.  45.     Complete  connection  for  the  operation  of  tube  with  in- 
duction coil  and  mercury  interrupter. 

cury  interrupter,  condenser,  oscilloscope,  valve  tube,  and 
series  spark  gap.  Note  that  the  milliammeter  is  next  to 
the  tube. 

When  the  spark  gap  is  placed  between  the  meter  and 
the  tube,  leakage  across  the  gap  may  make  the  reading 


98 


U.  S.  ARMY  X-RAY  MANUAL 


much  above  the  current  actually  passed  through  the  tube. 
Interrupters. — The  secondary  voltage  of  an  induction 
coil  is  the  result  of  change  of  current  in  the  primary.  It 
is  evident  that  we  cannot  have  the  primary  current  grow 
indefinitely,  so  we  must  allow  it  to  decrease  and  increase 
alternately.  The  value  of  the  secondary  voltage  for  a 
given  coil  depends  entirely  on  the  rate  at  which  the  primary 
current  is  changed.  Thus,  if  a  current  of  80  amperes 
should  be  reduced  to  0  amperes  in  .02  seconds,  the  current 


Pt.      Pb. 

INTERRURTER 

Fig.  46.     Wiring  for  induction  coil  with  electrolytic  interrupter. 

has  changed  at  a  mean  rate  of  4000  amperes  per  second. 
If  it  required  .04  seconds  for  the  same  change,  the  rate 
is  2000  amperes  per  second.  The  mean  secondary  voltage 
is  twice  as  great  in  the  former  case  as  in  the  latter. 

As  induction  coils  are  intended  to  operate  on  an  in- 
terrupted direct  current,  some  device  must  be  used  to  open 
and  close  the  circuit.  The  early  interrupters  were  of 
the  vibrating  hammer  type,  but  these  have  largely  been 
superseded  by  others  much  better  adapted  to  x-ray  work. 
They  are  still  used  on  small  outfits  where  large  power 
is  not  drawn. 


X-RAY  PHYSICS 


99 


The  Wehnelt  Interrupter. — The  Wehnelt  interrupter 
consists  of  a  lead  and  a  platinum  electrode  immersed  in  a 
solution  of  sulphuric  acid.  The  amount  of  platinum  ex- 
posed to  the  solution  is  usually  variable  at  will.  When 
connected  as  shown  in  Fig.  46,  the  application  of  sufficient 
voltage  will  result  in  the  formation  of  a  non-conducting 
layer  between  the  solution  and  the  platinum,  thus  inter- 
rupting current  flow.  The  layer  is  very  quickly  dissipated, 
reestablishing  current  only  to  be  again  formed,  etc.    When 

To  Motor 


VTTT^-'h 


Fig.  47.      Centrifugal  jet  mercury  interrupter. 

only  a  small  amount  of  platinum  surface  is  exposed,  the 
number  of  interruptions  per  second  is  high  and  the  cur- 
rent is  small.  Greater  immersion  lowers  the  number  of 
interruptions  and  draws  more  current. 

Operating  Notes. — 1.  The  solution  should  contain  30  to 
35  per  cent  pure  sulphuric  acid.  In  mixing,  be  sure  to 
add  small  amounts  of  acid  to  water,  allowing  the  mixture  to 
cool  after  each  amount  is  added.  Never  pour  water  into 
the  acid. 

2.  Do  not  iLse  a  condenser,  as  is  done  with  the  mechani- 
cal interrupter. 


100 


U.  S.  ARMY  X-RAY  MANUAL 


3.  If  your  point  or  points  are  adjustable,  use  little  or 
no  resistance  in  series  with  coil  and  interrupter  on  a 
110  volt  circuit. 

4.  Your  coil  may  not  have  the  correct  self-induction  for 
use  with  a  Wehnelt,  at  least  over  a  wide  range  of  fre- 
quencies of  interruption.  If  inverse  is  prominent,  try 
a  greater  amount  of  platinum  exposed,  thereby  lowering 
the  frequency  of  interruption. 

5.  Do  not  run  too  hot,  and  if  possible  enclose  inter- 
rupter in  a  sound-proof  box,  or  place  outside. 


Fig.  48.    **Eotax''  interrupter. 

6.  Be  sure  that  connections  are  made  to  the  proper 
terminals. 

7.  Do  not  try  to  operate  on  alternating  current  with- 
out a  rectifier.  This  has  been  done  in  a  few  instances, 
but  is  not  advised. 

The  Mercury  Interrupter. — ^Various  forms  of  inter- 
rupters using  mercury  have  been  invented,  and  have  some 
advantages  for  use  with  heavy  coils.  They  allow  varia- 
tion in  two  essential  particulars,  viz.,  number  of  inter- 
ruptions per  second  and  relative  duration  of  make  and 
break.     Two  forms  are  in  common  use.    In  the  jet  type, 


X-RAY  PHYSICS  101 

Fig.  47,  a  centrifugal  pump  throws  small  streams  of  mer- 
cury against  V-shaped  iron  terminals.  The  motor  speed 
determines  the  number  of  interruptions,  and  raising  or 
lowering  the  iron  decreases  or  increases  time  of  flow  rela- 
tive to  that  of  no  current. 

In  the  Rotax  interrupter,  Fig.  48,  the  mercury  is  thrown 
into  a  ring  revolving  with  the  case.  An  insulating  disc 
with  a  small  conducting  sector  is  mounted  so  that  it  may 
he  moved  to  and  from  the  circumference.  When  in  con- 
tact with  the  mercury,  the  disc  rotates  at  a  speed  depending 
on  the  mercury  speed  and  the  amount  of  immersion  of 
the  disc.  The  latter  is  insulated  from  the  case  and  is 
connected  to  an  external  binding  post.  The  relative  time 
of  current  ''on"  and  "off"  varies  with  the  immersion  of 
the  disc  in  the  mercury.  A  small  amount  of  paraffin  oil 
is  used,  forming  a  ring  inside  the  mercury  to  prevent 
oxidation,  A  better  plan,  when  the  apparatus  will  per- 
mit, is  to  use  illuminating  gas  in  the  case,  which  reduces 
contamination  of  the  mercury  and  enables  long  periods  of 
operation  without  refilling.  If  gas  is  used,  a  small  burner 
should  be  connected  to  the  cavity  and  kept  burning,  and 
the  current  should  never  be  turned  on  until  this  light 
continues  to  burn,  as  severe  explosions  may  result  by  spark 
ignition  of  an  air-gas  mixture.  Recent  forms  have  a 
safety  valve  to  protect  against  explosion. 

A  suitable  capacity  must  always  he  connected  to  the 
terminals  of  interrupters  of  this  type.  The  amount  of 
this  capacity  will  vary  with  different  inductances  of  the 
primary  and  to  some  extent  with  the  frequency  of  the 
interruption. 

Operating  Notes. — Carefully  read  and  preserve  any  di- 
rections furnished  by  the  maker  of  the  interrupter  used. 
If  none  are  at  hand,  and  trouble  arises,  some  one  or  more 
of  the  following  may  be  found  to  account  for  it. 


102  U.  S.  ARMY  X-RAY  MANUAL 

1.  No  current  in  any  position  of  the  disc.  Look  for 
poor  contacts,  either  from  bad  brush  on  revolving  case, 
loose  binding  posts,  or  broken  wires.  The  mercury  should 
be  examined  to  be  sure  that  there  is  enough  and  that  the 
oxide  does  not  prevent  contact. 

2.  Verif  heavy  primary  current  and  little  or  no  second- 
ary current  or  voltage.  Examine  capacity  to  see  if  it  is 
punctured ;  if  so,  renew  at  once.  If  condenser  is  all  right, 
see  if  disc  is  free  to  turn  and  is  not  immersed  too  far 
by  reason  of  an  overcharge  of  mercury. 

3.  Be  sure  to  keep  the  required  amount  of  oil  in  the 
case,  as,  if  there  is  too  little  it  becomes  carbonized  by  the 
arc  and  gives  trouble. 

4.  The  mercury  must  be  kept  clean.  When  it  is  dirty, 
oxidized,  or  emulsified  with  oil,  either  clean  by  filtering 
and  washing  or  put  in  new  mercury. 

A  coil  in  which  a  current  is  changing  always  develops 
an  active  opposition  to  the  alternation  of  current.  On  an 
attempt  to  increase  the  current,  the  coil  acts  as  an  op- 
posing generator,  and  when  current  falls  the  generator 
action  reverses.  This  action  is  due  to  self-induction.  The 
opposing  voltage,  when  we  change  current  at  the  rate  of  1 
ampere  per  second,  is  an  important  factor  in  behavior  of 
the  coil,  and  is  named  the  coefficient  of  self-induction. 

On  account  of  self-induction,  no  really  instantaneous 
change  of  current  can  take  place,  and  the  response  to 
variable  voltage  will  depend  on  this  feature  of  the  coil 
and  on  the  rate  at  which  we  attempt  to  make  current 
changes.  Each  coil  is  an  individual  in  this  respect,  and 
one  should  find  by  trial  the  conditions  under  which  it  op- 
erates best  for  each  purpose,  and  then  adhere  to  these 
conditions.  A  little  time  spent  in  this  way  will  save 
much  time  and  annoyance  later. 

Tubes  for  Use  with  Coils. — The   current  wave   from   a 


X-RAY  PHYSICS 


103 


coil  is  quite  different  from  that  from  a  transformer.    The 
current  consists  of  a  series  of  short  rushes  with  considerable 


Fig;  49.     Oscillogram — induction  coil  current  with  a  gas  mercury 
interrupter. 


Fig.  50.     Oscillograms — induction   coil   currents  with  Wehnelt  in- 
terrupter. 

time  between  each  impulse.  Fig.  49  shows  the  variations 
of  current  with  time  on  an  induction  coil  with  a  good 
mercury  interrupter.     Fig.  50,  two  curves  with  a  Weh- 


104  U.  S.  ARMY  X-RAY  MANUAL 

nelt  break.  Note  the  large  amount  of  inverse  in  the  latter. 
In  order  that  the  tube  current  may  not  lower  the  voltage 
belov/  the  required  point,  it  is  essential  to  have  gas  tubes 
at  relatively  high  vacuum,  or  hard.  Thus  we  must  have 
small  tube  currents. 

Readings. — Milliampere  and  spark  gap  readings  are  far 
less  reliable  guides  for  radiography  when  using  coils  than 
on  transformers.  The  gap  shows  peak  voltage  which  maj^" 
bfe  high  but  transient.  As  the  ordinary  milliammeter  indi- 
cates the  difference  between  direct  and  inverse,  one  may  get 
0  reading  and  yet  have  the  tube  operating. 

Portable  Coils. — Portable  coil  outfits  are  so  varied  as  to 
make  brief  description  impossible.  Those  heretofore  in  use 
were  largely  of  the  ' '  Tesla"  type. 

The  electric  lighting  current  is  stepped  up  to  about 
2000  volts  by  a  small  step-up  transformer,  if  the  supply 
is  from  an  alternating  current  line. 

If  the  current  is  direct,  the  circuit  is  made  and  broken 
by  some  form  of  vibrating  interrupter,  giving  much  the 
same  effect  in  the  transformer  as  though  an  alternating 
current  was  used. 

The  2000  volt  current  from  the  secondary  of  the  step-up 
transformer  charges  a  condenser.  The  condenser  is  dis- 
charged through  a  few  turns  of  wire  wound  around  the 
outside  of  a  secondary,  consisting  of  a  large  number  of 
turns  of  fine  wire.  The  discharge  of  the  condenser  is 
at  an  enormous  frequency,  and  high  voltages  of  high  fre- 
quency are  generated  by  the  Tesla  coil. 

As  the  current  delivered  by  the  Tesla  coil  is  alternat- 
ing, a  different  form  of  tube  must  be  used  from  that  for 
other  types  of  x-ray  generator,  if  best  results  are  de- 
sired. This  special  tube  has  a  valve  arrangement  built 
into  it  which  tends  to  suppress  one  wave  of  the  current. 

Fast  Work. — From  what  has  gone  before,  it  is  clear  that 


X-RAY  PHYSICS  105 

the  same  radiographic  density  can  be  secured  in  a 
great  variety  of  exposure  times.  Certainly,  for  the  in- 
experienced operator  high  speed  is  inadvisable.  If  3  to 
10  seconds  would  give  the  most  desirable  exposure,  an 
error  of  one  second  would  give  a  fairly  good  plate.  On 
power  such  that  i^  second  is  best,  an  error  of  one  second 
in  judgment  or  execution  would  exceed  the  latitude  of  the 
plate. 

The  conditions  for  fast  work  are: 

1.  Small  target-plate  distance. 

2.  Very  large  current. 

3.  High  voltage. 

4.  Fast  plates  or  intensifying  screens. 

The  disadvantage  of  the  first  is  distortion  and  haze 
of  outline,  due  to  size  of  electron  focus;  of  the  second 
danger  of  melting  the  target,  and  difficulty  in  setting 
to  proper  voltage.  "When  high  voltage  is  used,  the  even- 
ing up  of  penetration,  as  well  as  the  increase  of  scattering 
with  high  penetration  rays,  tends  to  give  flat  plates.  Very 
fast  plates  and  ordinary  plates  with  screens  allow  little 
latitude  of  exposure.  Screens  also  may  register  their  own 
dust  or  surface  defects. 

Photographic  Density  and  Character  of  Negative. — 
Considerable  objection  has  been  made  to  the  use  of  photo- 
graphic plates,  films,  or  paper  in  the  study  of  this  type 
of  radiation.  Much  of  the  adverse  criticism  is  well  founded, 
for  the  following  reasons:  The  unaided  eye  is  a  poor 
judge  of  comparative  absorption  of  light  by  a  negative; 
only  by  means  of  comparison  involving  photometric  appara- 
tus can  one  be  fairly  sure  of  correct  measurement.  If  an 
unexposed  or  clear  portion  of  a  negative  transmits  an  arbi- 
trary amount  of  light,  Q,  an  area  transmitting  50  per  cent 
or  half  as  much  would  be  said  to  have  an  opacity  of  2; 
and  the  logarithm  of  this  opacity  would  be  named  the 


106 


U.  S.  ARMY  X-RAY  MANUAL 


density  of  this  portion  of  the  negative.  It  has  been  found 
that  density  determined  in  this  way  is  proportional  to  the 
amount  of  silver  reduced  per  unit  plate  area.  Transmis- 
sions, opacities,  and  densities  are  related  as  follows : 


Transmission 

per 

cent 

Opacity 

Density 

0 

D 

100 

(Clear 

glass 

)  1 

0  (Log  1 

90 

10/9  — 1.11 

.104 

80 

10/8  —  1.25 

.223 

70 

10/7  —  1.43 

.358 

60 

10/6  —  1.66 

.507 

50 

10/5  —  2.00 

.693 

40 

10/4  —  2.50 

.916 

30 

10/3  —  3.33 

1.203 

20 

10/2  —  5.00 

1.609 

=  0) 


When  the  intensity 
and  quality  of  radiation 
remain  fixed,  the  expo- 
sure varies  only  with 
the  time.  Suppose  that 
Kt  =  E  where  K  de- 
pends on  the  nature  and 
intensity  of  the  radia- 
tion. Plotting  E  and  D, 
there  remains  a  line  ap- 
proximately as  shown  in 
Fig.  51.  A  portion  of 
this  line  AB  is  nearly 
straight;  below  A  and  above  B  it  is  curved  somewhat,  as 
shown.  If  AB  is  produced  to  cut  the  density  axis  at  7,  01 
is  named  the  inertia  of  the  plate.  The  portion  AB  of  the 
plot  is  the  region  of  proper  exposure.    Above  B  the  den- 


/  e 

Fig.  51.  The  relation  between  ex- 
posure and  density  of  a  photographic 
plate.  Below  A — underexposure.  Be- 
yond B — overexposure.  01 — inertia 
of  the  plate. 


X-RAY  PHYSICS  107 

sity  fails  to  increase  in  proportion  to  exposure  and  is  the 
region  of  over-exposure.  In  fact,  if  the  exposure  is  car- 
ried too  far,  the  density  falls  off  and  a  reversal  may  occur. 

The  slope  of  the  line  AB  or  the  ratio  BM/AM  ==  7 
is  named  the  development  factor:  For  under-develop- 
ment  7  is  small  and  contrast  is  low.  For  longer  de- 
velopment, the  line  swings  counter-clockwise  on  Z  as  a 
pivot.  The  point  where  one  should  stop  is  a  matter  to  be 
governed  by  experience.  In  ordinary  photography  7 
ranges  from  .8  to  1.3 ;  probably  no  accurate  determination 
can  be  made  of  the  most  desirable  conditions  until  some 
agreement  is  reached  as  to  the  best  quality  of  negative  for 
specific  purposes. 

The  inertia  of  the  plate  is  not  affected  by  time  of  de- 
velopment. A  fast  plate  is  one  where  01  is  small.  A  plate 
of  great  latitude  is  one  where  exposure  difference  for  A  and 
B  is  large.  The  speed  of  a  plate  is  determined  by  the 
inertia  01  and  is  expressed  in  arbitrary  sensitometer  units. 

The  conditions  during  development  fix,  for  a  given  plate, 
a  time  beyond  which  development  should  not  be  carried 
on  account  of  fog.  In  x-ray  work,  the  use  of  high  pene- 
tration on  thick  patients  tends  to  fog  by  cross  scattered 
radiation,  and  this  may  be  noticed  long  before  developer 
fog  becomes  troublesome. 

As  a  means  of  measurement,  we  may  utilize  different 
portions  ol  the  same  plate  under  different  physical  condi- 
tions to  learn  whether  the  radiation  effects  on  the  various 
portions  are  or  are  not  alike.  For  example,  if  a  constant 
voltage  is  used  at  constant  distance,  the  exposure  varies 
as  the  product  of  current  and  time — so  that  20  ma.  for 
2  seconds  and  40  ma.  for  1  second  should  give  equal 
density  with  equal  development,  provided  the  rise  and 
fall  of  voltage  be  alike  in  the  two  cases. 


108  U.  S.  ARMY  X-RAY  MANUAL 

Certain  terms  are  in  common  use  when  negatives  are 
described,  and  should  be  understood. 

Contrast  refers  to  the  amount  of  difference  in  darken- 
ing for  a  small  difference  of  exposure.  Thus,  if  rays  pass 
through  bone  and  flesh,  there  is  a  variation  in  the  amount 
of  radiation  reaching  the  plate,  due  to  difference  of  absorp- 
tion; when  this  results  in  a  marked  difference  in  darken- 
ing, the  negative  is  ' '  contrasty. ' '  Contrast  depends  on  the 
nature  of  the  plate  and  the  development,  and  to  a  great 
extent  on  the  quality  of  the  radiation  used.  If  the  beam 
is  too  penetrating,  contrast  is  reduced,  for  if  rays  pass 
through  bone  and  flesh  equally  well,  there  would  be  no 
contrast.  Too  ''soft"  radiation  will  fail  to  get  through 
the  denser  portion  and  will  give  high  contrast  but  poor 
detail  in  thick  parts.  The  amount  of  contrast  to  be  de- 
sired will  vary  with  the  work  to  be  done.  A  plate  showing 
fine  bone  detail  and  contrast  may  show  but  little  of  the 
soft  tissue. 

Detail  refers  to  the  fineness  of  the  marking  of  light  and 
shade.  Thus,  a  mastoid  plate  should  show  minute  struc- 
ture, or  lines  of  light  and  shade  should  show  sharp  grada- 
tion or  density  change.    Detail  depends  on: 

1.  Breadth  of  tube  focal  spot. 

2.  Distance  of  target  from  plate. 

3.  Distance  of  part  to  be  radiographed  from  plate. 

4.  Complete  immobilization  of  patient. 

5.  Correct  exposure  and  development. 

Exposure  Table. — Many  attempts  have  been  made  to 
work  out  exposure  tables  such  that  inexperienced  operators 
can  get  favorable  results.  Without  doubt  the  best  work 
is  done  when  spark  gap,  current,  and  time  are  chosen 
with  reference  to  the  individual  case  in  hand,  and  any 
operator  who  cannot  improve  on  the  results  secured  by 
adhering  to  any  single  table  is  unfit  for  the  work. 


X-RAY  PHYSICS 


109 


As  a  general  guide  in  starting  work,  a  uniform  rather 
high  gap  may  be  used — say  5  inches,  and  a  uniform  tar- 
get-plate distance — say  20  inches,  except  for  chest,  where 
28  inches  is  advised.  With  all  this  understood,  the  average 
of  reports  from  many  sources  gives  the  following  table 
for  a  patient  of  about  150  pounds  weight  and  a  Seed 
x-ray  plate.  Some  people  prefer  a  shorter  gap  for  most 
work  [p-a  head  work  excepted],  and  certainly  with  the 
ordinary  solid  tungsten  target,  medium  focus  Coolidge 
tube,  better  negatives  result  from  proper  exposure  on  a 
four-inch  gap  than  on  a  five-inch  one ;  this  will  require 
about  50  per  cent  increase  in  time  of  exposure  for  the 
same  distance  and  current. 


Part                    Time :  sec. 

Head,  A-P 

12 

Head,  Lat. 

6 

Neck 

3 

Shoulder 

31/2 

Elbow 

11/2 

All  exposures  on  5"  gap, 

Wrist 

1 

40  ma.  20"  distance  ex- 

Kidney 

3     5 

cept  chest,  which  is  at 

Bladder 

3     5 

28". 

Hip  joint 

5    7 

Pelvis 

5    7 

Knee 

2 

Ankle 

11/2 

Lumbar  spine 

5     6 

Teeth  (slow  film) 

4 

Teeth   (fast  film) 

11/2 

Chest    (at  28") 

21/2     4 

Notes:  (a)  For  parts  above  average  thickness,  increase 
time  considerably  more  than  in  proportion  to 
increase  of  thickness. 


110  U.  S.  ARMY  X-RAY  MANUAL 

(b)  If  it  is  necessary  to  work  at  other  distances 
than  20",  use  the  following  table  of  multiply- 
ing factors: 

Distance  Time  factor  Distance  Time  factor 

15''                       .6  21''                       1.1 

16  .6  22                        1.2 

17  .7  23                        1.3 

18  .8  24                        1.4 

19  .9  25                        1.6 

20  1.0 

For  ** Diagnostic  plates,"  reduce  time  by  %.  For  dou- 
ble coated  Eastman  films  use  half  the  time. 

With  intensifying  screens  no  fixed  rule  can  be  given.  A 
reduction  factor  may  be  found  for  the  screen  used  as 
indicated  on  pages  112-114. 

Plates  and  Films. — Photographic  plates  and  films  con- 
sist of  a  thin  layer  of  gelatin  containing  a  salt  of  silver 
and  spread  on  glass  or  celluloid.  Light  and  x-rays  cause 
a  change  in  the  silver  salt  such  that  suitable  chemicals, 
called  developers,  act  on  the  portions  that  have  received 
the  radiation,  changing  the  silver  compound  to  metallic 
silver,  and  thus  rendering  those  portions  more  or  less 
opaque  to  light.  The  opacity  produced  will  depend  on  the 
amount  of  radiant  action,  on  the  sensitiveness  of  the  emul- 
sion, and  on  the  development.  Those  portions  receiving 
much  light  or  x-rays,  when  fully  developed,  may  be  quite 
opaque;  other  portions  may  be  entirely  or  nearly  trans- 
parent. 

After  development  the  plate  is  washed  and  placed  in  a 
'* fixing''  bath  which  removes  the  unused  silver  salt,  as 
shown  by  the  disappearance  of  the  cream  color  of  the  emul- 
sion, rendering  the  parts  not  radiated  and  developed  trans- 
parent. 


X-RAY  PHYSICS  111 

All  plates  sensitive  to  x-rays  are  also  sensitive  to  ordi- 
nary light  and  hence  they  must  be  entirely  protected  from 
ordinary  white  light  until  finished. 

The  emulsion  is  an  example  of  unstable  chemical  struc- 
ture and  may  be  injured  by  (1)  moisture,  (2)  high  tem- 
perature, (3)  contact  with  other  material,  (4)  exposure 
to  light  or  x-rays,  (5)  bending.  Plates  should  be  kept  in 
the  original  boxes,  on  edge,  in  a  cool  dry  room,  well  pro- 
tected from  x-rays.  No  more  plates  should  be  put  up  in 
envelopes  than  are  likely  to  be  used  in  the  next  two  or 
three  days. 

Filling  Envelopes  and  Cassettes. — X-ray  plates  are  used 
either  in  envelopes  or  in  plate-holders,  called  cassettes. 
It  is  quite  essential  that  in  regular  work  the  emulsion  side 
should  be  toward  the  patient.  To  insure  this  when  using 
envelopes,  arrange  the  envelopes  to  be  filled  before  darken- 
ing the  room.  Put  black  and  yellow  envelopes  in  alterna- 
tion with  the  end  flaps  down,  insert  plate  with  emulsion  side 
down,  i.  e.,  so  that  the  flap  will  fold  over  the  hack  of  the 
plate ;  then  insert  the  flap  end  first  in  the  yellow  envelope 
with  the  emulsion  down,  so  that  the  flap  of  the  outer  en- 
velope also  folds  over  the  back.  Then  place  the  smooth 
side  of  the  envelope  toward  the  target.  A  soft  brush 
is  useful  to  remove  dust  from  plates  and  cassettes. 

In  using  cassettes  without  screens,  put  the  emulsion  side 
down.  This  side  can  be  determined  by  sighting  across  the 
surface,  as  it  appears  dull  as  compared  with  the  glass  side, 
or  touching  the  tongue  to  the  extreme  corner  of  the  plate — 
the  emulsion  side  will  be  slightly  sticky.  Form  the  habit 
of  closing  partly  empty  plate  boxes  at  once  after  filling 
envelopes  or  cassettes. 

Attention  is  called  here  to  the  new  double-coated  film 
which  is  used  to  considerable  extent.  In  this  case  there 
is  no  difference  in  the  two  sides  of  the  film  and  no  at- 


112  U.  S.  ARMY  X-RAY  MANUAL 

tention  need  be  paid  in  placing  it  in  the  special  holders 
provided.  It  should  be  borne  in  mind,  however,  that  these 
films  must  be  handled  with  great  care.  Finger  prints  are 
much  more  likely  to  show  and  both  sides  of  the  emulsion 
must  be  prot3cted  from  moisture  and  scratches.  Great 
care  must  also  be  taken  not  to  wrinkle,  bend  or  twist 
these  films  before  exposure.  For  this  reason  it  is  undesir- 
able to  attempt  to  use  them  in  the  ordinary  black  or  yellow 
envelopes  usually  supplied.  They  should  be  used  in  cas- 
settes or  in  the  special  holder  furnished  for  the  purpose. 

Intensifying  Screens. — When  using  intensifying  screens 
the  usual  practice  in  this  country  is  to  allow  the  rays  to 
pass  through  the  glass  to  the  emulsion  and  then  to  the 
screen  surface.  Consequently  the  negative,  when  viewed 
with  the  emulsion  side  toward  the  eye,  is  reversed  as  to 
right  and  left  as  compared  with  the  usual  plate.  The 
screen  should  be  firmly  fixed  to  the  back  of  the  cassette 
and  should  be  kept  scrupulously  clean;  wipe  off  dust 
with  a  clean  cloth,  and  never  touch  the  surface  with  wet  or 
greasy  fingers.  Insert  cleaned  plate  with  emulsioyi  side  up, 
and  be  sure  that  the  springs  press  the  screen  firmly  against 
the  plate.  On  account  of  the  variable  x-ray  opacity  of  the 
glass  at  present  in  use,  screen  work  with  plates  is  rather 
uncertain.  Be  sure  to  keep  screen  clean  by  not  letting  it 
get  wet,  dirty,  or  dusty. 

It  is  quite  impossible  to  be  sure  of  the  speed  of  the  vari- 
ous screens  in  actual  use,  inasmuch  as  this  depends  on 
so  many  conditions,  such  as  amount  of  use,  and  the  general 
care  which  has  been  exercised  in  handling,  as  well  as  their 
initial  speed. 

In  order  that  the  proper  exposure  may  be  given  it  is  well 
to  determine  the  multiplying  factor  by  which  the  screen 
increases  the  normal  speed  of  the  plate.  This  may  be 
easily  done  by  the  use  of  a  film  of  proper  size  in  the  screen 


X-RAY  PHYSICS  113 

holder,  exposed  at  the  same  time  with  one  in  an  ordinary 
envelope  or  container  laid  on  top  of  the  screen.  This  en- 
velope should  be  cross-ruled  with  lines  approximately  I/2 
inch  apart,  and  a  heavy  sheet  of  lead  placed  to  cover  all 
except  one  end  division,  being  sure  that  film  occupies  this 
division.  Make  a  very  brief  exposure  at.  low  power  and 
considerable  distance,  using  a  timer,  if  one  is  available, 
and  leaving  the  tube,  machine,  timer  and  distance  un- 
changed; slide  the  sheet  of  lead  back,  leaving  two  divi- 
sions exposed;  and  repeat  the  exposure.  Do  this  for  all 
of  the  film  and  develop  both  films  at  the  same  time  and 
in  the  same  developer. 

It  will  be  evident  that  if  there  were  15  divisions,  the 
one  which  was  exposed  first  received  15  exposures,  the 
next  14,  etc.  The  last  may  be  numbered  1,  the  next  2, 
etc.  If  it  should  be  found  that  the  film  in  the  envelope, 
and  not  affected  by  the  intensifying  screen,  required  12 
of  these  exposures  to  give  the  same  blackening  as  number 
one,  with  the  intensifying  screen,  it  is  clear  that  1/12  of 
the  time  required  with  no  screen  should  be  used.  This 
procedure  is  somewhat  more  reliable  if  exposures  can  be 
through  a  rectangular  block  of  paraffin,  as  the  speed  of 
some  screens  seems  to  vary  considerably  according  to  the 
filtration  which  the  rays  have  received  before  reaching  the 
emulsion.  Fig.  52  shows  such  a  pair  of  films  for  a  particu- 
lar screen.  After  the  determination  of  the  speed,  it  should 
be  marked  on  the  cassette  so  as  to  be  available  during 
use. 

Care  in  Handling  Plates  and  Films. — In  all  cases,  plates 
and  films  must  be  kept  well  protected  by  lead  when  in  the 
x-ray  room.  A  good  lead-lined  box  on  casters  is  very  use- 
ful for  this  purpose,  and  where  much  work  is  done,  one  for 
exposed  and  another  for  unexposed  plates  should  be  pro- 


114 


U.  S.  ARMY  X-RAY  MANUAL 


vided,  or  a  partition  plainly  marked  "EXPOSED''  and 
"UNEXPOSED,"  dividing  a  single  box  may  be  used. 


Fig.  52.     Gradation   due   to   successive   equal   exposures  with   and 
without  intensifying  screen,  a,  without  screen,  h,  with  screen. 

The  following  cautions  may  be  given  to  those  unfamiliar 
with  darkroom  work: 

1.    Never  handle  plates  or  films  with  wet  or  greasy  fin- 


X-RAY  PHYSICS  115 

gers,  either  before  or  after  exposure.     Marks  and  streaks 
are  sure  to  result,  even  if  the  emulsion  is  not  destroyed. 

2.  Learn  to  handle  plates  without  touching  the  emulsion 
side,  even  with  dry  fingers. 

3.  Mix  all  solutions  according  to  instructions  and  see 
that  chemicals  are  actually  dissolved. 

4.  Keep  all  trays  clean,  and  do  not  use  insufficient  or 
too  old  developer;  stains  are  hard  to  remove,  and  the  cost 
in  time  and  money  is  excessive  if  it  is  attempted. 

5.  In  tray  development,  be  sure  that  the  developer  cov- 
ers the  entire  plate  at  once.  Tilt  the  tray  slightly  on  insert- 
ing the  plate,  and  tilt  the  tray  in  several  directions  to 
ensure  complete  wetting  of  the  film  as  soon  as  possible. 
Keep  tray  in  motion  during  development. 

6.  Do  not  examine  the  plate  by  removing  it  from  the 
developer  until  the  minimum  time  for  full  development  on 
normal  exposure  has  elapsed. 

7.  Do  not  try  to  develop  several  plates  in  a  tray  at  one 
time  if  they  overlap. 

8.  Wash  negatives  well  on  removing  from  the  developer, 
before  placing  in  the  fixing  bath. 

9.  Leave  negatives  in  the  fixer  for  some  minutes  after 
they  seem  to  be  fully  cleared;  then  wash  thoroughly,  in 
running  water  if  possible. 

10.  Do  not  use  the  same  trays  for  hypo  and  for  devel- 
opment. Mark  hypo  trays  and  keep  them  well  away  from 
developer.    A  little  hypo  in  the  developer  is  fatal. 

11.  Keep  negatives  in  a  dust-free  atmosphere  and  in 
one  location  and  position  until  dry. 

12.  When  the  developer  is  not  in  use,  keep  in  tightly 
closed  containers.  Glass  fruit  jars  with  rubbers  are  as 
good  as  anything  for  small  amounts.  Use  a  close-fitting 
float  in  tank. 

13.  Don't  try  all  the  developing  formulas  you  can  find; 


116  U.  S.  ARMY  X-RAY  MANUAL 

take  one  advised  for  the  plate  you  use,  and  learn  to  use  it. 

14.  Don't  fix  in  plain  hypo  in  warm  weather.  Plates 
will  frill  if  you  do. 

Tank  Development. — In  tank  development,  the  plate  is 
placed,  while  dry,  in  a  special  frame  or  holder  and 
hung  vertically  in  the  tank  containing  the  developer.  This 
method  is  desirable  when  much  work  is  done.  With  strong 
developer,  stirring  by  moving  the  holders  will  prevent 
vertical  streaks. 

Temperature. — The  action  of  the  developer  varies 
greatly  with  changes  in  temperature.  Between  60°  F. 
(16°  C.)  and  70°  F.  (22°  C.)  is  best.  Hot  developer  works 
fast  and  is  likely  to  fog  the  plate.  Cold  developer  is  slow 
and  may  not  give  anything  on  a  normal  exposure.  Do  not 
cool  developer  by  adding  ice  or  ice  water,  as  this  dilutes 
the  solution.  When  using  tanks,  cold  or  ice  water  may 
flow  or  stand  around  the  developer  tank  until  a  proper 
temperature  is  reached,  or  put  ice  in  a  fruit  jar  and 
immerse  jar  in  developer. 

Concentration. — If  more  water  is  added  to  a  normal 
developer,  slower  action  will  result.  This  is  sometimes  ad- 
vised in  tank  development,  and  with  screen  plates,  but 
is  not  necessary  if  the  developer  is  stirred  occasionally. 

Plate  Defects. — Plates  are  sometimes  defective,  due  to 
faults  or  accidents  in  manufacture,  but  in  most  cases  of 
complaint  the  trouble  is  due  to  improper  treatment  after 
leaving  the  factory.  If  one  is  sure  of  proper  exposure, 
development,  fixation  and  washing,  and  still  finds  streaks, 
spots,  bubbles,  or  bad  color,  the  plates  may  be  blamed. 
Much  trouble  is  traced  to  the  materials  used  at  present, 
and  in  all  cases  of  doubt  check  plates  should  be  made. 
Defects  are  not  likely  to  appear  on  the  same  region  in 
both  negatives.  Looking  across  the  negative  at  any  un- 
evenly illuminated  surface  will  often  show  whether  a  spot 


X-RAY  PHYSICS  117 

is  due  to  a  defect  in  the  glass  or  to  something  on  the  emul- 
sion surface. 

Examining  Negatives. — When  it  can  be  avoided,  plates 
ought  not  to  be  examined  until  dry.  If  they  must  be 
used  while  wet,  care  is  needed  to  avoid  heating  the  gela- 
tin or  it  will  melt  and  completely  ruin  the  negative.  A 
well-diffused  illumination  is  very  desirable;  it  should  be 
well  under  control  so  as  to  give  a  strong  light  for  dark  nega- 
tives and  a  much  weaker  one  for  thin  ones.  Ground  or  opa- 
lescent glass  is  not  needed  if  a  dull  white  surface  is  illumi- 
nated and  the  plates  are  viewed  by  light  reflected  from  it. 
Fig.  53  shows  a  useful  type  of  illuminator. 

Developer  Action. — The  action  of  developer  on  an  ex- 
posed plate  is  rather  a  complicated  matter.  For  the  pres- 
ent purpose  we  may  omit  discussion  further  than  to  say 
that  with  any  active  developing  agent  a  suitable  amount 
of  alkali  is  indispensable.  Do  not  vary  the  proportion 
shown  in  reliable  and  tested  formulae,  at  least  in  routine 
work.  Development  at  any  given  depth  below  the  surface 
of  the  emulsion  can  only  take  place  when  the  active  de- 
veloping solution  has  reached  that  point  in  sufficient 
amount  to  cause  the  change  required.  Hence,  dilute  or 
partly  exhausted  developer  requires  more  time.  Prolonged 
action  of  developer  on  the  emulsion  will  cause  a  darkening 
even  with  little  or  no  exposure,  and  too  strong  developer 
will  over-develop  the  outer  layers  before  the  deeper  ones 
are  affected.  Plates  exposed  to  x-rays  are  developable 
through  the  entire  depth  of  emulsion,  while  light  only  af- 
fects the  outer  layer.  Hence,  if  fog  can  be  avoided,  x-ray 
plates  will  increase  in  density  with  longer  development  to 
a  greater  extent  than  will  negatives  exposed  to  light.  The 
action  of  potassium  bromide  restrains  or  delays  develop- 
ment at  the  surface  and  tends  to  keep  the  ''whites"  clear. 
All  developers  are  absorbers  of  oxygen  and  are  useless  when 


118 


U.  S.  ARMY  X-RAY  MANUAL 


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X-RAY  PHYSICS  119 

they  no  longer  absorb  this  gas.  For  this  reason,  they  ought 
to  be  protected  from  air  when  not  in  use. 

"Hypo"  or  Fixing. — The  purpose  of  fixation  is  the  re- 
moval of  all  unreduced  silver,  leaving  the  small  specks  of 
metallic  silver  suspended  in  the  gelatin  film.  Any  unre- 
duced silver  left  in  the  gelatin  will  sooner  or  later  discolor 
and  ruin  the  negative.  By  using  acid  and  alum,  the  clear- 
ing is  improved  and  the  film  of  gelatin  hardened.  ' '  Hypo ' ' 
must  be  thoroughly  removed  by  washing  half  an  hour  to 
one  hour  in  running  water,  so  that  hypo  crystals  will  not 
form  in  the  gelatin,  ruining  the  negative.  If  the  bath 
is  too  acid  a  rash  will  appear  on  the  surface  of  the  gela- 
tin. The  acid  should  be  partly  neutralized  by  the  addition 
of  sodium  carbonate.  If  the  bath  appears  milky,  it  gener- 
ally lacks  acid  and  can  be  cleared  by  the  addition  of  acetic 
acid. 

Fog. — It  is  extremely  important  for  every  roentgenol- 
ogist to  realize  the  full  effect  of  fog  produced  on  the  nega- 
tive in  development.  This  fog  is  the  result  of  chemical 
action  and  is  always  produced  to  a  certain  extent.  It  is 
not  uniformly  distributed  over  the  plate  in  any  case,  and 
is  related  to  a  certain  extent  to  the  exposure  at  the  points 
where  it  shows.  It  has,  always,  the  effect  of  blotting  out 
the  finer  details.  In  a  properly  exposed  and  developed 
plate  these  finer  details  show  as  light  areas  against  a  slight- 
ly darkened  background,  as,  for  example,  in  the  case  of  a 
mastoid  plate. 

As  soon  as  fog  is  produced  to  such  an  extent  that  these 
clear  white  lines  become  smoky,  contrast  with  the  slightly 
darker  background  and  adjacent  areas  may  be  entirely  lost. 
Fog  will  always  be  produced  if  the  developer  is  too  warm, 
if  improperly  mixed,  or  if  the  time  of  development  is  too 
long.  The  only  way  to  avoid  it  for  a  given  plate  is  to 
use  a  proper  concentration  of  the  developer,  a  proper  tern- 


120  U.  S.  ARMY  X-RAY  MANUAL 

perature,  and  such  an  exposure  as  will  enable  complete 
development  to  be  made  before  fogging  action  becomes  ef- 
fective. 

The  roentgenologist  should  invariably  remember  that  a 
proper  distribution  of  shadows  on  his  plate  or  fluoroscopic 
screen  furnishes  the  only  physical  basis  for  diagnostic  use 
of  his  radiation,  and  to  avoid  the  necessity  of  passing  upon 
indefinite  and  unsatisfactory  plates  it  is  just  as  essential  to 
pay  attention  to  the  darkroom  conditions  as  it  is  to  consider 
proper  position  and  exposure.  The  diagnoses  made  on  the 
basis  of  shadows  that  are  so  faint  as  to  be  invisible  to  the 
majority  of  observers  introduce  a  very  considerable  ele- 
ment of  imagination,  and  are  relatively  unsafe  even  for 
those  who  claim  successful  results  on  such  a  basis. 

Developing  Formulae. — Most  x-ray  operators  had  been 
using  a  hydrochinon-metol  developer  prior  to  the  shortage 
of  metol.  Certain  substitutes  for  metol  have  been  marketed 
of  more  or  less  value.  The  following  formulae  have  been 
found  fairly  good  in  practice : 

Hydrochinone — 

"Water  (warm)    1       gal.         5       gal. 

Sodium  sulphite  (dry)   .  .   8       oz.         40       oz. 

Hydrochinone  IVs    "  TVs  '' 

Sodium  carbonate  (dry)      8        ''  40       '' 

Pot.  bromide  1       dr.  5       dr. 

Mix  in  order  named. 

Good  for  tank  development. 

Elon-Hydrochinone — 

(Dissolve  these  chemicals  in  order  named:) 

Water 20  oz. 

Elon    20  grs. 

Sulphite  of  soda  (dry) 1  oz. 

Hydrochinone 80  grs. 


X-RAY  PHYSICS  121 

Carbonate  of  soda  (dry) 1  oz. 

Potassium  bromide 8  grs. 

Good  for  tank  development. 

Edinol-Hydrochinone — 

Solution  A 

Boiling  distilled  water 32  oz. 

Sodium  sulphite  (dry)    6  oz. 

Edinol   5  dr. 

Hydroehinone    1  oz. 

Potassium  bromide   6  dr. 

Solution  B 

"Water 32  oz. 

Potassium  carbonate  2  oz. 

Use  one  ounce  of  Solution  A,  one  ounce  of  Solution  B 
and  two  ounces  of  water.    Develop  6  to  9  minutes. 

Good  for  tray  development. 

Metabisulphite-Hydrochinone.— A  professional  photog- 
rapher doing  considerable  x-ray  development  recommends 
the  following  developer  as  very  satisfactory  for  general 
work: 

Mix  in  order  named. 

Solution  A 

Water  200  oz. 

Hydroehinone   .  . .  ., 4  oz. 

Potassium  metabisulphite    10  gr. 

Potassium  bromide    50  grs. 

Solution  B 

Water  200       oz. 

Sodium  sulphite I14  lbs. 

Caustic  soda 2i/4  oz. 

These  solutions  keep  well  in  stock.     For  use,  mix  in 
equal  parts. 


122  U.  S.  ARMY  X-RAY  MANUAL 

Fixing  Bath  Formulae. — An  acid  hypo  fixing  bath  may- 
be prepared  as  follows: 

Water  64  oz. 

Hypo 16  oz. 

When  fully  dissolved  add  the  following  hardening  solu- 
tion: 

Water   5  oz. 

Sulphite  of  soda 1  oz. 

Acetic  acid  (28%  pure) 3  oz. 

Powdered  alum 1  oz. 

If  preferred,  1  ounce  of  citric  acid  may  be  substituted 
for  acetic. 

This  bath  may  be  made  up  at  any  time  in  advance  and 
may  be  used  so  long  as  it  retains  its  strength,  or  is  not 
sufficiently  discolored  hy  developer  carried  into  it  to  stain 
the  negatives. 

Chrome  Alum  Fixing  Bath. — This  bath  has  good  keep- 
ing qualities,  fixes  clean  and  remains  clear  after  long  con- 
tinued use. 

A 

Pure  water 96  oz. 

Hypo    . 2  lbs. 

Sulphite  of  soda 2  oz. 

B 

Pure  water 32  oz. 

Chrome  alum 2  oz. 

Sulphuric  acid,  C.  P i/4  oz. 

Mix  chemicals  in  order  named. 

When  dissolved,  slowly  pour  B  into  A  while  stirring  rap- 
idly. 

Notes  on  Fixing. — ^Hypo  is  cheaper  than  spoiled  plates. 
Use  plenty  and  renew  often.  Wash  all  plates  very  thor- 
oughly to  remove  hypo. 


X-RAY  PHYSICS  123 

Do  not  strengthen  an  old  weak  hypo  bath.  Throw  it 
away  and  make  a  new  one.  It  may  fix,  but  it  is  sure  to 
spoil  plates  sooner  or  later. 

Failure  to  wash  off  developer  will  quickly  spoil  a  fixing 
bath. 

Stained  plates  are  usually  due  to  one  or  more  of  the  fol- 
lowing causes: 

Too  warm  developer. 

Too  long  development  of  under-exposed  plates. 

Exhausted  hypo  bath. 

Lack  of  acidity  of  the  hypo  bath. 

Reducing  Dense  Negatives — 

Solution  No.  1 

"Water  16  oz. 

Potassium   f erricyanide 1  oz. 

Solution  No.  2 

Water  16  oz. 

Hypo 1  oz. 

Place  plate  in  Solution  No.  2  sufficient  to  cover  it,  then 
add  a  small  quantity  of  No.  1,  and  watch  it  carefully.  If 
it  reduces  too  slowly,  add  more  of  No.  1.  If  only  too 
dense  in  places,  apply  the  solution  carefully  with  a  brush 
or  tuft  of  cotton. 

Wash  in  running  water  at  least  a  half  hour  after  re- 
ducing. 

Note. — Make  negative  properly  and  avoid  reduction. 

Darkroom. — The  first  consideration  in  a  darkroom  is  the 
complete  exclusion  of  ordinary  light.  All  windows,  cracks, 
knot  holes,  key  holes,  etc.,  must  be  stopped  by  opaque  ma- 
terial. If  possible,  an  entrance  by  corridor  or  winding 
way  should  be  used.  If  a  door  is  used  it  should  fasten  on 
the  inside,  so  that  no  one  can  open  it  at  an  inopportune 
time. 


124 


U.  S.  ARMY  X-RAY  MANUAL 


The  usual  emulsion  on  x-ray  plates  is  quite  insensitive 
to  red  or  orange-red  light.  A  very  small  intensity  of 
blue  or  white  light  will  ruin  a  plate.  The  quality  of  light, 
not  the  amount,  is  what  must  be  considered,  and  enough 
of  a  safe  light  may  be  used  to  see  clearly  what  one  is 
doing  without  danger  of  fogging  a  plate,  if  the  operator 
is  not  too  slow.  The  inner  walls  of  the  room  should  be 
painted  red  or  orange,  not  black.  A  ruby  20-watt  lamp, 
four  or  five  feet  above  the  working  shelf  with  a  translu- 
cent shade  below  it  covered  with  postoffice  paper,  will 
give  a  diffuse  illumination  of  the  room  very  desirable  for 


Fig.  54.  Simple  arrangement  of  light  for  developing.  The  slide 
contains  a  white  and  a  ruby  glass  with  yellow  (P.O.)  paper  between. 
A  clear  lamp  is  used. 

work.  Test  the  light  by  placing  an  opaque  object  on  a 
small  plate.  Expose  on  the  shelf  for  two  minutes  and 
develop  full  time;  if  not  fogged,  the  light  is  safe  for  that 
make  of  plate.  If  one  desires  to  time  development  by  look- 
ing through  the  plate,  an  arrangement  as  shown  in  Fig. 
54  or  one  as  sold  by  some  dealers  is  desirable.  By  using  a 
flexible  cord,  the  lamp  in  Fig.  54  may  be  hung  outside  after 
the  box  is  opened  and  serve  as  the  source  to  be  used 
when  no  plates  are  exposed  to  light. 

Arrangement. — Darkrooms  may  be  quite  elaborate  and 
yet  be  very  inconvenient.  A  simple  arrangement  for  a 
small  outfit  is  shown  in  Fig.  55.  No  doors  are  needed  in 
this  case. 

Fixing  bath  and  supplies  are  to  be  kept  apart  from  de- 


X-RAY  PHYSICS 


125 


veloper  and  developing  supplies.  A  plain  open  shelf  is  used 
in  filling  envelopes,  etc.  Cassettes,  intensifying  screens, 
and  envelopes  may  be  kept  in  suitable  compartments  below. 
Plates  in  small  amounts  may  be  kept  in  compartments 
above  this  shelf.     An  inexpensive  arrangement  serving  all 

HYPO.    INLET    ,DEV, 
\     ±      / 


FIXINQ  SUPPLIES 
SINK 


5: 

i 


o 

I 


OEVBLOPfNG 
SUPPLiES 


PLATES  BELOW 


J 


CASSETTES  ^ND 
ENVELOPES  BELOW- 


DRYING  RACK 


FAN 


J 

1 


PLATE 

LOAD- 
ING 
SHELF 

24"^ 


IN 


Tig.  55.     A  convenient  darkroom  arrangement. 


needs  is  shown  in  Fig.  56  for  holding  developer  tank,  fixing^ 
tank,  and  also  serving  as  a  washing  tank.  For  a  perma- 
nent installation  the  tank  may  be  lead-lined,  but  for  a 
semipermanent  wooden  tank  a  heavy  coating  of  water  and 
chemical-proof  paint  will  suffice.  In  warm  weather,  use  ice 
to  cool  bath,  and  do  not  dilute  developer. 

Ventilation. — Good  ventilation  is  essential  in  a  dark- 
room, not  alone  to  increase  the  efficiency  of  the  operator, 


126 


U.  S.  ARMY  X-RAY  MANUAL 


but  because  a  close,  musty  atmosphere  is  bad  for  tbe  sensi- 
tive emulsion.  When  a  new  room  is  designed,  the  matter 
is  quite  simple,  but  when  any  old  closet  is  regarded  as  good 


HYPO 


WASH 


INL£T 

RIN5E 


DPveLOP^ff] 


Fig.  56.  Wooden  tank  to  permit  circulation  of  water  around  de- 
veloper and  fixer,  provides  for  rinsing  and  washing  films  or  plates 
at  same  temperature  throughout. 

enough  for  a  darkroom  it  is  quite  a  different  matter.     The 
important  point  to  be  kept  in  mind  is  that  air  must  be  let 


Bracket 


Fig.  57.     Simple  ventilator  for   darkroom, 
be  painted  red  or  black. 


All  inner  surfaces  to 


in  and  out,  but  light  must  be  excluded.  Where  an  electric 
fan  can  be  used,  it  is  easy  to  accomplish  this  result.  Fig.  57 
shows  one  way.     The  fan  is  placed  in  a  box,  open  at  each 


X-RAY  PHYSICS  127 

end,  inserted  through  the  wall.  A  second  box  is  placed 
inside  the  room,  as  shown,  and  all  surfaces  are  painted  a  flat 
black.  Air  has  free  passage,  and  light  is  entirely  excluded. 
A  similar  arrangement  can  be  used  in  a  window,  either  with 
or  without  the  fan. 

Humidity. — Basement  darkrooms  are  often  very  damp 
in  summer  and  very  hot  in  winter.  The  best  work  cannot 
be  expected  under  these  conditions.  If  such  must  be  used, 
it  is  best  to  keep  unused  plates  elsewhere. 

Care  of  Utensils. — ^Absolute  cleanliness  is  essential  in 
darkroom  work.  Trays  not  in  use  are  best  kept  filled  with 
water.  Be  sure  that  no  acid  gets  into  the  developer.  Do  not 
use  developer  or  fixing  tanks  painted  inside  with  any  kind 
of  water-proof  paint. 

Supplies. — Be  careful  to  keep  all  containers  labeled,  so 
that  no  mistakes  are  likely  to  be  made.  Keep  hypo  and 
acids  away  from  developer  material.  Keep  chemicals  pro- 
tected from  moisture.  Remember  that  twice  the  weight  of 
crystals  must  be  used  as  in  case  of  ' '  dry ' '  materials. 

Marking  Negatives. — ^Where  a  large  amount  of  radio- 
graphic work  is  done,  a  well-organized  record  system  is 
indispensable.  In  all  cases  the  record  should  show  in  some 
way  on  the  negative,  and  that  record  must  be  put  on  before 
the  plate  is  developed.  Lead  numbers  may  be  used,  and 
if  this  is  done  the  number  used  and  the  name  of  the  patient 
must  he  entered  on  a  suitable  card  or  hook  at  the  time  the 
exposure  is  made. 

If  numbers  are  not  used,  a  slip  showing  the  name  of 
the  patient  must  be  attached  to  the  cassette  or  envelope, 
and  the  darkroom  operator  should  always  write  the  name 
with  a  soft  pencil  on  one  corner  of  the  emulsion  before 
development. 

In  using  double-coated  film  care  should  be  taken  to  mark 
right  and  left,  as  one  cannot  tell  how  the  film  was  placed. 


128  U.  S.  ARMY  X-RAY  MANUAL 

The  X-Ray  Negative. — The  conditions  which  determine 
the  distribution  of  shadows  on  an  x-ray  negative  are  ex- 
tremely complex  and  vary  with  the  physical  condition,  age, 
and  weight  of  the  patient  even  without  any  reference  to 
pathological  conditions.  If  there  were  no  material  between 
the  target  and  the  photographic  emulsion,  there  woiild 
result,  upon  exposurt  and  development,  simply  a  uniform 
blackening  of  the  plate.  The  introduction  of  material  in 
the  path  of  the  radiation  between  the  target  and  the  plate 
results  in  absorption  and  scattering  with  the  result  that 
portions  of  the  emulsion  are  protected  from  the  radiation, 
the  resulting  shadow  showing  as  a  white  or  lighter  area 
by  transmitted  light  through  the  negative.  The  amount 
of  radiation  failing  to  reach  any  area  of  the  plate  as 
compared  with  that  reaching  the  surface  of  the  obstructing 
body  depends  upon  two  things:  first  upon  the  relative 
physical  density  of  the  material  traversed  as  compared 
with  its  immediate  surroundings  and,  second,  upon  the 
distance  in  this  material  of  greater  or  lesser  density 
actually  traversed  by  the  rays.  As  an  illustration,  the 
shadow  cast  by  a  thin,  flat  bone,  placed  with  its  surface 
parallel  to  the  plate  will  show  little  contrast  as  compared 
with  the  shadow  of  the  surrounding  flesh,  whereas,  if 
placed  on  edge,  increasing  the  path  traversed  in  the  bone, 
there  will  be  marked  contrast. 

In  traversing  the  human  body  radiation  passes  through 
an  aggregate  made  up  of  portions  of  decidedly  different 
densities.  Each  of  these  portions  absorbs  the  radiation 
in  an  amount  depending  both  on  its  density  and  thick- 
ness. When  we  further  take  into  account  the  physical 
nature  of  the  action  of  the  photographic  plate  and  the 
different  absorbability  of  the  radiation  under  different 
conditions  of  tube,  we  may  easily  recognize  the  reason 
for  the  variety  of  negatives  which  it  is  possible  to  secure  of 


X-RAY  PHYSICS  129 

the  same  anatomical  region.  Inasmuch  as  our  diagnostic 
information  must  be  acquired  from  a  study  of  these  areas, 
we  must  not  forget  that  pathological  conditions  are  liable 
to  be  inferred  if  based  upon  doubtful  or  imperfect  data, 
and  while  we  can  not  at  present  lay  down  complete  rules 
for  the  guidance  of  the  roentgenologist  it  is  undoubtedly 
true  that  for  each  individual  area  there  is  a  combination 
of  factors  of  exposure,  penetration,  development,  and 
position,  that  would  give  the  best  diagnostic  plate. 

Consider  the  effect  of  varying   (1)   the  quality  of  the 
x-ray   beam,    (2)    the   time   of   exposure   when   making  a 
negative  of  any  particular  region.     Assuming  that  we  have 
proper  development  of  the  plate  after  exposure,  we  may 
note  that  if  the  tube  has  a  small  equivalent  gap  the  major- 
ity of  the  radiation  will  be  absorbed  completely  by  even 
thin  and  non-dense  portions  of  the  patient,  and  that  the 
exposure  in  order  to  have  any  effect  on  the  plate  must 
be  prolonged.     For  example,  in  the  case  of  the  hand,  such 
a  tube  with  proper  exposure  may  bring  out  wrinkles  or 
folds  in  the  flesh,  finger  nails,  and  a  very  slight  infiltra- 
tion in  the  soft  tissues,  and  only  by  prolonged  exposure 
can    even    a   moderate    definition    of   bones    be    observed. 
When  this  is  done  the  parts  of  the  negative  covered  by 
soft   tissue   afe   greatly   overexposed.      If   the   spark   gap 
is  too  small  nothing  but  a  shadow  of  the  hand  such  as 
would  be  cast  by  ordinary  light  will  be  observed.     As  we 
change  the  spark  gap  with  a  suitable  time  of  exposure 
we  can  secure  quite   different   qualities  of  negative  and, 
with   a  moderate   gap   and   exposure,   fair   details   in  the 
bone    and    the    soft    tissue    may   be    observed,    but,    with 
longer  exposure,  portions  of  the  plate  beneath  the  thinner 
or  softer  regions  still  become  overexposed,  giving,  on  de- 
velopment,   complete   blackness   without    details.     At  the 
same  time  the  outlines  of  the  thicker  portions  and  of  the 


130  U.  S.  ARMY  X-RAY  MANUAL 

bones  may  stand  out  very  clearly,  giving  almost  the  ap- 
pearance of  a  skeleton. 

If  the  spark  gap  is  made  too  high  the  radiation  reach- 
ing the  plate  may  be  only  modified  to  a  slightly  greater 
extent  by  the  bones  than  by  the  soft  tissue,  and  we  get  a 
characteristic  plate,  lacking  in  contrast,  which  is  generally 
described  by  the  term  ^'flat."  In  an  extreme  case,  nearly 
all  of  the  radiation  might  pass  through  the  body  with 
only  a  trifling  amount  of  absorption,  and  there  would  be 
no  differentiation  with  reference  to  density  and  thickness 
upon  the  plate.  Consequently,  while  no  complete  guide 
can  be  given,  the  general  effect  of  increased  spark  gap  is 
to  reduce  the  contrast,  and  the  general  effect  of  increased 
exposure  with  moderate  gap  is  to  obliterate  the  details  in 
the  soft  tissue  or  thin  portions  with  an  increase  in  the 
visibility  of  the  shadows  cast  by  the  denser  or  thicker 
portions.  If,  for  example,  one  desires  a  study  of  the 
thoracic  vertebrse,  one  must  expect  that  portions  of  the 
plate  receiving  radiation  through  the  air-filled  lungs  will 
be  greatly  overexposed  and  will  indicate  no  shadows. 
With  a  softer  tube,  details  of  the  spine  and  ribs  will  be 
less  obvious,  while  the  linear  markings  in  the  chest  are 
rendered  visible.  It  naturally  follows  that  tube  condi- 
tion and  exposure  should  be  adapted  to  bring  out  the 
information  desired.  Mention  may  also  be  made  of  the 
fact  that  the  overexposed  and  denser  regions  may  fre- 
quently give  valuable  information  if  viewed  with  a  suffi- 
ciently strong  source  of  light,  while  a  thin  negative,  or 
those  portions  in  which  the  shadows  are  faint  and  the 
total  blackening  slight,  are  best  observed  in  weak  light. 

Inference  as  to  pathology  can  only  be  safely  made  when 
due  account  is  taken  of  the  variation  in  the  shadows  due 
to  normal  variation  in  human  anatomy  and  the  procedure 
followed  in  making  the  negative. 


X-RAY  PHYSICS 


131 


o 


O  Form  551 

Medical  Department,  U.  S.  Army 
(Revised  July  19,  1917) 

CLINICAL   RECORD 

RADIOGRAPHIC  REPORT 


Station. 

Date 

From 

To 


Information   requested:. 


Clinical  diagnosis: 


Laboratory 

X-ray  findings: 


PLATE 


NUMBER  SIZE 


191 


.,  U.  S.  Army. 


.,191 


PART  DISPOSITION 


,  U.  S.  Army. 

SURNAME  OF  PATIENT 

CHRISTIAN  NAME 

RANK 

COMPANY 

REGIMENT  OR  STAFF  CORPS 

Fig.  58.     Eecord  and  report  form  for  x-ray  examination    (actual 
size  Sy^  ins.  x  8  ins.). 


132  U.  S.  ARMY  X-EAY  MANUAL 

Records. — The  importance  of  the  correct  recording  of 
all  information  obtained  by  means  of  the  x-ray  cannot  be 
overestimated.  Of  equal  or  greater  importance  is  the 
establishment  of  the  identity  of  the  patient  examined  with 
the  x-ray  findings.  Furthermore,  the  identity  of  the  side 
examined  should  be  verified  in  every  case. 

That  the  x-ray  findings  are  brought  to  the  attention  of 
the  attending  surgeon  is  essential.  An  actual  conference 
between  the  surgeon  and  the  roentgenologist  is  very  desir- 
able in  order  that  each  may  have  the  advantage  of  the 
other's  personal  opinion. 

Each  plate  should,  therefore,  be  marked  for  identifica- 
tion by  means  of  opaque  markers  and  the  corresponding 
information  immediately  recorded  on  the  blanks  provided 
for  this  purpose. 

Form  551  Medical  Department,  U.  S.  Army  (Revised 
July  19,  1917),  will  be  used  for  this  purpose,  Fig.  58.  In 
all  cases  a  duplicate  of  this  report  should  be  retained. 


LABORATORY  EXPERIMENTS 

Laboratory  Instruction  in  Preparation  for  Roentgenol- 
ogy.— The  following  experiments  are  part  of  a  series  used 
in  the  laboratory  course.  They  were  easier  of  execution 
in  the  laboratory  in  which  they  were  devised,  and  results 
were  more  conclusive,  on  account  of  having  a  very  good  high 
tension  voltmeter  so  that  tube  voltage  measurements  could 
be  accurately  and  quickly  made. 

The  objects  of  such  experiments  are: 

1.  To  give  practice  in  quickly  adjusting  machine  and 
tubes  to  any  desired  current  and  voltage. 

2.  To  impress  on  the  mind  of  the  student  the  relation 
of  the  fundamental  factors — voltage,  current,  distance  and 
time — to  the  nature  of  image  desired. 

3.  To  assure  the  operator  that  results  are  reproduci- 
ble if  conditions  are  right. 

4.  To  show  some  of  the  pitfalls  usually  encountered 
and  to  avoid  having  to  acquire  experience  on  the  living 
patient. 

While  at  first  such  experiments  may  seem  very  time- 
consuming,  experience  has  shown  that  the  skill  and  con- 
fidence acquired  will  much  more  than  repay  it  in  a  com- 
paratively short  time. 

New  students,  and  even  those  of  some  experience,  are 
likely  to  have  trouble  in  handling  the  apparatus  if  it  has 
many  unusual  details.  They  should,  therefore,  read  such 
paragraphs  of  the  manual  as  deal  with  the  elementary 
principles,  before  starting  experimental  work. 

133 


134  U.  S    ARMY  X-RAY  MANUAL 

The  Coolidge  tube  is  used  in  these  experiments  on 
account  of  its  easy  adjustn^ent.  Experience  indicates  that 
when  taking  the  same  current  at  the  same  voltage  all  tubes 
give  very  much  the  same  density  of  negatives,  so  that  ex- 
posures learned  on  the  Coolidge  tube  apply  to  the  gas  tube 
in  so  far  as  the  conditions  can  be  made  the  same. 

Experience  in  the  training  of  a  considerable  number 
of  students  has  clearly  shown  that  the  handling  of  x-ray 
apparatus  cannot  he  learned  by  seeing  some  one  else  do  it. 
Only  when  the  students  have  repeatedly  carried  on  the 
actual  manipulations  themselves,  time  after  time,  can  they 
be  depended  upon  under  working  pressure.  Much  time 
is  lost  in  not  knowing  just  what  exposures  should  be  given 
and  the  test  plates  described  are  excellent  checks  on  accu- 
racy and  rapidity.  The  student  should  be  well  drilled  in 
quickly  setting  the  tube  and  control  for  definite  readings. 
In  the  study  of  plates  as  well  as  in  the  technical  work 
the  student  should  do  absolutely  individual  and  independ- 
ent work. 

Instruction  Unit. — A  small  instruction  unit  has  been 
devised  to  clearly  set  forth  the  basic  principles  of  the  large 
x-ray  machines  and  to  avoid  unnecessarily  tieing  up  ex- 
pensive equipment  for  elementary  instruction  purposes. 
This  machine  is  composed  of  only  the  customary  elements 
and  these  are  arranged  on  an  ordinary  pine  table  so  that 
all  parts  and  all  wires  are  completely  in  view  and  readily 
accessible.  For  instruction  purposes  high  power  is  un- 
necessary, a^d  a  small  transformer  is  ample  for  the  pur- 
pose. With  the  transformer  used,  loads  up  to  5-inch  gap, 
30  ma.,  may  be  safely  drawn  for  test  plate  and  other 
experimental  work.  The  autotransformer,  rheostat,  fila- 
ment transformer,  timer,  etc.,  are  standard  parts  as  used 
on  the  large  machines,  so  that  the  student  may  become 
familiar  with  their  function  and  operation. 


LABORATORY  EXPERIMENTS      135 

It  is  intended  to  have  the  machine  as  simple  as  it  is 
possible  to  make  it,  and  to  this  end  the  various  circuits 
are  distinguished  from  each  other  by  the  color  of  wire 
used.  Thus,  the  main  primary  circuit  is  black,  the  motor 
circuit  is  blue,  the  Coolidge  filament  primary  is  red,  and 
the  remote  control  circuit  is  green.  Even  to  a  beginning 
student  the  circuits  stand  out  separate  and  distinct,  and 
the  machine  appears  organized  and  rational  rather  than 


j  ^//amtnt  /^imary  Circuit' 


Fig.  59.     Diagram   of    connections  of   instruction   unit. 


a  hopeless  maze  of  wiring.  Fig.  59  shows  the  diagram 
of  connections  and  Fig.  60  shows  the  machine  itself.  Su- 
perfluous parts  have  been  eliminated  and  the  features 
shown  are  so  fundamental  that  each  student  should  be 
able  to  wire  up  the  complete  machine  as  part  of  his  labora- 
tory work. 

Aside  from  giving  a  knowledge  of  the  electrical  elements 
of  x-ray  machines,  the  unit  is  used  to  give  considerable 
practice  in  setting  for  any  desired  tube  voltage  and  milli- 
amperage,  in  operating  when  failure  of  some  non-essential 


136  U.  S.  ARMY  X-RAY  MANUAL 

element  occurs,  and  in  studying  the  physical  properties  of 
the  x-rays. 

Test  Plates. — The  quantitative  measurement  of  x-ray 
radiation  has  proved  a  difficult  matter,  but  for  our  pur- 


FiG.  60.     Machine  used  for  instruction  purposes.     All  parts  and 
wiring  are  openly  displayed. 


pose  the  photographic  effect  is  sufficiently  accurate  and 
determines  the  usefulness  of  the  rays  in  practice. 

We  cannot  readily  compare  the  radiation  received  on 
two  spots  of  unequal  density.  Under  any  conditions  of 
operation,  however,  if  two  portions  of  a  photographic 
plate  subjected  to  radiation  and  given  the  same  develop- 


LABORATORY  EXPERIMENTS  137 

ment  have  equivalent  blackening"  we  may  say  that  the 
two  parts  received  the  same  quantity  of  photographically 
effective  radiatiom  per  unit  area,  or  that  they  had  the 
same  exposure,  in  which  case  exposure  does  not  mean 
time  alone. 

If  a  spot  exposed  1  second  and  a  spot  exposed  2  sec- 
onds are  of  equal  darkness,  then  we  can  say  that  the 
first  spot  was  subjected  to  radiation  twice  as  intense  as 
the  second,  for  it  took  only  half  as  long  to  give  equal 
effect.  The  spots  should  not  be  heavily  overexposed .  or 
over-developed,  for  it  is  in  the  medium  gray  tones  that 
distinctions  in  density  are  most  accurately  and  easily 
made. 

A  5  X  7  plate  is  cased  in  the  usual  envelope  or  in  a 
light-tight  plate  holder.  The  student's  name,  laboratory 
number  and  the  number  of  the  experiment  should  be 
written  on  the  emulsion  side  of  the  plate  with  soft  lead 
pencil  when  loading.  A  5  x  7  lead  plate  with  ten  1- 
inch  holes  is  used  to  protect  the  body  of  the  plate  from 
radiation  and  all  holes  except  the  one  spot  to  be  ex- 
posed are  covered  with  sheet  lead.  Expose  the  test  spots 
in  proper  sequence  down  the  two  rows  of  holes,  and  place 
a  small  metallic  marker  on  spot  No.  1  during  exposure  to 
identify  it  later. 

In  using  a  timer  do  not  vary  its  settings,  as  the  scales 
are  rarely  calibrated  with  sufficient  accuracy.  Keep  the 
timer  set  at  0.1  second  and  repeat  the  exposure  the  re- 
quired number  of  times.  If  the  machine  is  not  equipped 
with  a  timer  capable  of  conveniently  repeating  1/10  sec- 
ond exposures,  time  with  a  stop  watch  or  by  counting 
to  full  seconds  instead  of  tenths.  Increase  considerably 
the  target-plate  distance  in  this  case,  if  possible. 

Do  not  develop  test  plates  too   far.   Stop  as  soon  as 


138  U.  S.  ARMY  X-RAY  MANUAL 

spots  Nos.  1  to  5  show  fairly  well  on  the  back  of  the 
plate.  If  the  settings  have  been  carefully  made  and  ex- 
posures accurately  timed,  spots  Nos.  1  to  5  should  be  ap- 
proximately equal  in  density  and  Nos.  6  to  10  should 
run  successively  darker  or  lighter  as  the  case  may  be. 

When  the  finished  plates  are  dry  the  spots  should  be 
numbered  and  all  exposure  data  written  on  the  emulsion 
side  of  the  plate  with  pen  and  ink.  The  plate  should 
then  be  turned  in  for  inspection  and  credit. 

Before  commencing  work  read  and  understand  the  gen^ 
eral  instructions  and  precautions  on  page  20. 

Distance-Time  Relation — Inverse  Square  Law. 

Test  Plate  1. — The  x-rays  travel  out  from  the  electron 
impact  point  on  the  target  in  straight  lines,  so  that  the 
amount  in  a  cone  of  a  given  angle  is  spread  over  an  in- 
creasing base  area  as  we  recede  from  the  tube.  A  plate  of 
fixed  size  intercepts  more  radiation  in  a  given  time  when 
close  to  the  source.  If  we  move  a  plate  to  double  its  origi- 
nal distance  from  the  target,  the  radiation  received  per  sec- 
ond on  a  given  area  will  be  only  %  as  great;  at  ten  times 
the  distance,  1/100  as  great.  In  order  to  secure  the  same 
radiation  effect,  the  time  of  reception  must  be  increased 
four-fold  in  the  first  case  and  one  hundred  fold  in  the 
latter. 

For  constant  tube  current  and  voltage  the  plate  black- 

tlTYlft 

ening   will   be   unchanged   if  we   keep      : —     con- 
distance  ^ 

stant  for  all  exposures. 

Set  for  10  ma.  at  a  3-inch  spark  gap  and  expose  spots 
as  shown  below.  Or  the  bedside  unit  may  be  used,  ex- 
posing seconds  instead  of  tenths. 


LABORATORY  EXPERIMENTS  139 

Spot  Spot 


No. 

Distance 

Time 

No. 

Distance 

Time 

1 

10  in. 

.1  sec. 

6 

10  in. 

.1  sec, 

2 

20" 

.4  '' 

7 

20" 

.1  " 

3 

30" 

.9  " 

8 

30" 

.1  " 

4 

40" 

1.6  " 

9 

40" 

.1  " 

5 

50" 

2.5  " 

10 

50" 

.1  " 

In  the  first  row  of  spots  we  have  compensated  for  the 
change  in  distance  by  a  proper  corresponding  change  in 
time,  so  these  spots  will  have  the  same  density.  In  the 
second  row  we  have  made  no  such  compensation  and 
the  spots  will  not  be  equally  dark.  The  target-plate  dis- 
tances ordinarily  used  in  radiographic  work  vary  from 
15  to  36  inches.  The  sharpness  of  the  radiograph  increases 
with  greater  distance,  but  longer  time  is  required.  As- 
suming that  1  second  is  the  correct  exposure  for  a  given 
object  at  20  inches,  plot  a  curve  on  cross  section  paper 
showing  time  required  at  various  distances  up  to  36  inches 
to  give  the  same  density  of  plate. 

Current-Time  Relation. 

Test  Plate  2. — The  x-ray  energy  on  a  given  plate  area 
per  unit  time  when  the  voltage  is  constant  and  the  target- 
plate  distance  is  fixed,  increases  in  direct  proportion  to  the 
current.  Thus,  we  get  the  same  radiation  in  half  the  time 
when  using  50  ma.  as  when  using  25  ma.  Or,  for  equal 
photographic  effect  the  product  of  milliamperes  and  sec- 
onds must  remain  constant. 

To  test  this  law  expose  a  test  plate  as  follows : 

Voltage  constant  at  a  4-inch  gap. 

Target-plate  distance  constant  at  30  inches. 


140  U.  S.  ARMY  X-RAY  MANUAL 


Spot 

Current 

Time 

Spot 

Current 

Tim 

1 

5  ma. 

1.2  sec. 

6 

5  ma. 

1.2    S6 

2 

10    " 

.6  " 

7 

10    " 

1.2  " 

3 

15    " 

.4  '^ 

8 

15    " 

1.2  '' 

4 

20    " 

.3  " 

9 

20    '' 

1.2  '' 

5 

30    " 

.2  '^ 

10 

30    " 

1.2  " 

Notice  that  we  have  compensated  by  a  decrease  in  time 
for  the  increase  in  current  in  the  first  row  and  that  the 
second  row  is  uncompensated. 

Voltage-Time  Relation. 

Test  Plate  3. — The  radiation  leaving  a  given  target  as 
registered  by  a  photographic  plate  is  not  fixed  by  the 
amount  of  current  alone,  but  varies  greatly  with  the  drop 
in  voltage  through  the  tube.  In  fact,  it  increases  very 
nearly  in  proportion  to  the  square  of  the  voltage.  This 
means  that  on  doubling  the  voltage,  all  other  factors  re- 
maining unchanged,  we  get  four  times  the  photographi- 
cally effective  radiation  per  second  and  would  then  need 
but  one-fourth  the  exposure  time. 

With  an  electrostatic  high  tension  voltmeter  it  is  easy 
to  read  voltage  directly,  but  this  instrument  is  not  ordi- 
narily available.  The  so-called  primary  ''kilovoltmeters'' 
with  which  many  machines  are  equipped  are  not  reliable 
indicators  of  secondary  voltage,  as  they  do  not  read  the 
same  for  the  same  secondary  voltage  under  different  loads 
on  the  transformer.  Parallel  sparking  distance  between 
blunt  points  is  our  best  available  guide  to  tube  voltage. 
The  relation  between  spark  length  and  kilovolts  is  shown 
in  Fig.  12.    It  may  be  considered  as  reasonably  true  that 


LABORATORY  EXPERIMENTS 


141 


under  average  conditions  the  kilovoltage  is  ten  times  the 
spark  in  inches  plus  ten,  i.  e.,  3-inch  gap  =  40  kv. ;  Si/g-inch 
gap  =  65  kv.,  etc. 

Exposures  are  to  be  made  as  follows: 

Current  constant  at  5  ma. 

Distance  constant  at  25  inches. 


Spot       Gap 

Time 

Spot 

Gap 

Time 

1       2''   (30  kv. 

)       1.6  sec. 

6 

2''  (30  kv. 

)       1.6  sec 

2      3"  (40    "  ; 

)         .9    '' 

7 

3"   (40    "  ] 

)       1.6    '' 

3       4"   (50    "  ] 

)          .6*" 

8 

4"   (50    "  [ 

)       1.6    '' 

4       5''   (60    "  \ 

)         .4    '' 

9 

5''  (60   "  ; 

)       1.6    '' 

5       6''   (70    ''  ] 

)          .3*'' 

10 

g„   (70    ''  ; 

)       1.6    " 

*  These  figures  are  fair  approximations  to  the  exact  values. 

The  equality  of  density  of  numbers  1  to  5  as  well  as 
the  great  density  difference  of  numbers  6  to  10  illustrate 
well  the  effect  of  increased  voltage. 

It  must  not  be  assumed  that  the  quantity  of  radiation 
alone  varies  with  the  voltage  at  constant  current  and  time. 
The  ability  to  pass  ihrough  material  also  increases  to  a 
great  extent  at  higher  voltage.  The  quality  of  negatives  of 
the  same  average  density  made  at  high  and  at  low  voltage 
is  quite  different  and  a  voltage  (penetration)  suitable  for 
the  case  in  hand  should  be  chosen  if  the  best  results  are  to 
be  secured. 


Summary  of  the  Preceding  Relations 

Test  Plate  4. — Formulating  the  experience  derived  from 
the  preceding  experiments,  we  may  conclude  that  for  a 
given  tube  and  machine— i.  e.,  a  fixed  wave  form,  fre- 
quency, target,  and  absorbing  glass  wall — we  may  regulate 


142  U.  S.  ARMY  X-RAY  MANUAL 

the  exposure,  when  no  absorbing  material  is  traversed,  by- 
control  of  (a)  current,  (b)  voltage,  (c)  time,  (d)  dis- 
tance. 

Expressed  in  algebraic  form,  the  photographic  effect  E 
is  given  by 

^ ^  X  Current  x  (Voltage)  ^  x  Time 

(Distance)^ 
where  K  may  change  for  various  targets,  glass  walls,  or 
wave  form,  but  is  fixed  for  a  given  tube  and  outfit.  If  this 
is  true,  one  can  readily  compute  from  one  set  of  condi- 
tions the  length  of  time  under  other  conditions  that  will 
give  the  same  plate  density. 

To  calculate  the  time  for  a  given  exposure  use  simple 
approximate  methods,  not  long  and  involved  computations. 
Thus,  if  a  case  is  given  as  follows: 
Exposure  1 : 

50   ma. — 5-inch   gap — 18   inches — 4   seconds. 
Exposure  2: 

15   ma. — 4-inch   gap — 27   inches — time  =    ? 
Decrease  in  current  increases  time  10/3  times. 
Increase  in  distance  increases  time  9/4  times. 
Decrease  in  gap  increases  time  25/16  =  3/2 
Then  the  required  time  is 

5 
-X — x-x-  =  45  seconds. 

Start  with  4-inch  gap  10  ma.  20-inch  target-plate  dis- 
tance, and  .2  sec.  Calculate  and  expose  11  spots  so  as  to 
vary  two  or  three  of  the  above  factors  each  time,  but  keep 

(4)"  x  10  x  2 
E  constant,    E  =  ^-^-- =-.  .08  arbitrary  units  for  spot 


LABORATORY  EXPERIMENTS 


143 


No.  1.  Thus,  if  current  is  raised  to  30  ma., 
this  increase  would  give  a  time  %  as  great;  but  if 
the  distance  is  raised  to  30  inches  the  greater  distance  would 
require  a  time  9/4  as  great.  Hence  the  correct  time  with 
the  combined  change  is  .2  x  l^  x  9/4  =  .15. 

Do  not  work  below  a  2-inch  gap  on  account  of  the  absorp- 
tion of  the  glass  walls  of  the  tube,  or  on  the  small  instruc- 
tion units  above  5  ma.  on  a  6-inch  gap  or  above  30  ma.  on 
a  smaller  gap. 

Use  a  variety  of  control  buttons,  and  where  the  timer 
will  not  give  exact  results,  get  as  near  as  possible  or  vary 
one  or  more  factors  to  get  exact  tenths.  The  timer  will 
not  give  smaller  fractions  with  any  considerable  accuracy. 

The  exposures  are  to  he  computed  before  coming  to  the 
laboratory. 

Enter  your  results  as  follows : 


No, 

MA. 

Gap. 

Distance 

Time 

1 

10 

4// 

20'' 

,2  sec. 

2 

5 

5'' 

25'' 

? 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

144  U.  S.  ARIVIY  X-RAY  MANUAL 

If  correctly  done,  no  variation  in  darkening  will  be  ob- 
served. 

Change  in  Time  of  Exposure  with  Thickness 

Test  Plate  5. — Exposure  Factor.  Find  by  trial  the  ra- 
tio of  the  time  required  to  get  the  same  density  through 
one  layer  of  a  paraffin  as  when  no  absorber  is  present.  To 
do  this,  expose  a  plate,  using  a  machine  setting  of  10  ma., 
3-inch  gap ;  or  use  the  bedside  unit,  exposing  seconds  in- 
stead of  tenths  and  giving  the  plate  much  shorter  develop- 
ment.    Use  17-inch  distance  for  all  spots. 


Spot 

Layers  of 

Time 

Spot. 

Layers  of 

Time 

No. 

Paraffin 

No. 

Paraffin 

1 

0 

.1 

6 

1 

.4 

2 

0 

.2 

7 

1 

.5 

8 

0 

.3 

8 

1 

.6 

4 

1 

.2 

9 

1 

.7 

5 

1 

.3 

10 

1 

.8 

When  the  plate  is  developed  compare  other  spots  with 
Nos.  1,  2  and  3,  and  select  the  pair  that  comes  closest  to  an 
exact  match  in  density.  If,  for  example,  spots  No.  1  and 
5  are  equally  dark,  the  exposure  factor  is  determined  by 
the  ratio  of  the  time  of  exposure  used — in  this  instance,  3. 

This  factor  can  be  checked  by  comparing  spots  No.  2  and 
8,  which  should  match  if  the  factor  is  3. 

A  method  similar  to  this  can  be  used  to  obtain  the  speed 
ratio  of  intensifying  screens,  exposing  part  of  a  plate  with 
a  screen  and  part  without,  as  suggested  elsewhere  in  the 
manual.  Fig.  52,  page  114. 

Absorption  of  rays  and  scattering  gives  an  explanation 
of  the  great  increase  in  time  of  exposure  with  increasing 


LABORATORY  EXPERIMENTS  145 

thickness  of  absorbing  layer.  Thus,  if  experiment  shows 
that  a  certain  thickness  of  a  given  material  will  reduce 
the  emerging  radiation  to  3/5  the  incident,  then  a  spot  ex- 
posed through  this  layer  will  require  5/3  the  time  for  the 
same  photographic  density  as  the  uncovered  portion  of  the 
plate  would  require.  For  two  such  layers  25/9  the  orig- 
inal time  will  be  required,  for  three  layers  125/27,  etc. 


Fig.  61.     Effect    of    scattering    on  undercutting  of  image. 
{Test  Plate  6).     Using  the  factor  obtained  from  Test 
Plate  5  and  the  law  indicated  above,  calculate  proper  ex- 
posure times  and  expose  the  plate  as  follows : 

Machine  setting  constant  at  10  ma.,  3-inch  gap,  30-inch 
distance;  or  use  the  bedside  unit,  if  it  was  used  for 
Test  Plate  5,  again  exposing  seconds  instead  of  tenths  and 
giving  the  plate  short  development. 


Spot 

Layer  of 

Time 

Spot 

Layer  of 

Tim 

No. 

Paraffin 

No. 

Paraffin 

1 

0 

.3 

6 

0 

.3 

2 

1 

•  • 

7 

1 

.3 

3 

2 

•  • 

8 

2 

.3 

4 

3 

•  • 

9 

3 

.3 

5 

4 

•  • 

10 

4 

.3 

146  U.  S.  ARMY  X-RAY  MANUAL 

The  time  for  proper  exposure  in  order  to  get  the  best 
plate  does  not  work  out  from  the  simple  law  of  absorp- 
tion. The  reason  is  clear  when  we  consider  scattering 
in  tissue.  Let  AB,  in  Fig.  61,  be  a  small  object  in  the 
body,  relatively  opaque  to  x-rays.  If  there  were  no  scat- 
tering, the  area  S  would  be  protected  from  radiation  by  an 
amount  fixed  by  the  increase  in  absorption  of  AB  over  that 
of  an  equal  amount  of  tissue.  Thus,  if  volume  represented 
by  1,  2,  3,  4  would  absorb  95  per  cent  when  AB  is  absent, 
then  if  the  object  were  entirely  opaque  it  could  only  reduce 
exposure  by  5  per  cent  of  that  adjacent  to  it.  In  addition, 
all  the  shaded  portions  of  the  figure  are  sending  scattered 
radiation  to  ;S'  in  proportion  to  what  each  point  receives. 
To  reduce  this  scattering  as  much  as  possible  no  more  of 
the  body  should  be  exposed  than  is  necessary,  and  condi- 
tions maintained  to  give  as  high  contrast  as  possible.  The 
best  plates  of  thick  parts  are  rarely  of  high  density  as 
compared  with  those  of  extremities.  Contrast  is  always 
better  when  the  gap  is  made  as  low  as  possible,  consistent 
with  other  operating  conditions. 


The  Benoist  Penetrometer 

Test  Plate  7. — X-rays  are  caused  by  the  violent  change 
in  the  speed  of  electrons,  and  the  quantity  and  quality  of 
the  beam  will  depend  on  the  number  of  electrons  involved, 
their  speed,  and  the  suddenness  of  their  stop.  By  quality, 
we  should  specify  the  relative  intensity  of  each  wave 
length.  As  the  operating  voltage  is  increased,  there  is  a 
great  increase  in  the  electron  velocity.  Thus  Ev  ^  % 
MV^,  where  E  is  the  electronic  charge,  v  the  voltage,  M 
the  mass  of  the  electron,  and  V  its  speed. 


LABORATORY  EXPERIMENTS 


147 


There  is  no  way  of  easily  analyzing  a  beam  and  so  the 
ability  of  the  shorter  waves  to  pass  through  material  is 
used  to  give  a  rough  idea  of  the  quality.  This  penetration 
is  only  approximately  indicated  by  a  penetrometer.  The 
Benoist  penetrometer  may  be  used  to  test  out  exposures  and 
to  secure  a  more  accurate  knowledge  of  the  factors  govern- 
ing plate  density  than  can  be  easily  acquired  otherwise. 

Use  a  lead  cover  having  twelve  holes  to  take  a  fairly 
large  penetrometer.  Use  sheet  lead  to  cover  parts  of  plates 
not  being  exposed.  Remove  the  holder  from  the  table  and 
cover  all  portions  while  adjustments  are  made,  in  order  to 
avoid  fogging.  Take  considerable  care  in  adjusting  the 
tube,  and  note  carefully  the  exposures  specified.  Study 
your  plate  and  see  how  it  checks  out  with  the  computed 
times  for  equality  of  density  as  far  as  the  blackening  under 
the  silver  is  concerned. 

Silver  is  approximately  a  non-selective  absorber  for  the 
range  of  wave  lengths  used  in  practice,  while  the  aluminum 
absorbs  ''soft"  rays  in  excess.  Read  the  "hardness"  by 
noting  the  number  of  the  aluminum  sector  that  gives  the 
same  photographic  density  as  the  silver.  That  sector  giv- 
ing the  highest  plate  density  is  called  No.  1,  and  the  others 
number  consecutively.  Discuss  carefully  the  difference  seen 
in  the  negative.  Make  the  following  exposures  with  fairly 
careful  settings. 

Target-plate  distance,  15  inches. 


Row  1 

Row  2 

Row  3 

Ma. 

Gap 

Time 

Ma. 

Gap 

Time 

Ma. 

Gap 

Time 

10 

2" 

1.2 

10 

2" 

1.2 

10 

2" 

1.2 

15 

2" 

.8 

10 

3" 

.7 

15 

3" 

.4 

20 

2" 

.6 

10 

4" 

.4 

20 

4// 

.2 

25 

2" 

.5 

10 

5" 

.3 

25 

5" 

.1 

148  U.  S.  ARMY  X-RAY  MANUAL 

Tabulate  the  Benoist  hardness  and  voltmeter  readings, 
also  plot  on  cross  section  paper.  What  relation  exists  in 
the  incident  radiation  among  the  above  exposures  ? 

The  longer  wave  lengths  are  absorbed  in  excess,  and 
the  remainder  of  the  beam  as  transmitted  contains  an  ex- 
cess of  short  waves.    Such  a  beam  is  said  to  be  filtered. 

Note. — The  Benoist  penetrometer  is  not  a  very  useful 
or  reliable  guide  as  to  tube  quality — ^not  nearly  so  satis- 
factory in  transformer  operation  as  spark  gap ;  but  it  does 
serve  to  give  an  idea  of  penetration  difference  if  one  is 
sure  that  the  same  qvxmtity  falls  on  the  instrument  in  each 
case. 


NEW   APPARATUS 

In  the  following  pages  of  this  manual  there  will  be  de- 
scribed some  new  apparatus  and  appliances  which  have 
been  developed  with  advice  of  many  roentgenologists  and 
surgeons  with  the  sole  intent  of  aiding  the  service.  This 
apparatus  was  not  designed  to  secure  novelty,  or  simply  to 
be  different  from  other  devices,  but  with  a  view  of  secur- 
ing, first,  simplicity  and  convenience,  second,  elimination 
of  error  and  unnecessary  steps  and,  third,  to  secure  manu- 
facture at  such  a  rate  as  will  enable  the  product  to  be 
used  at  the  earliest  possible  moment. 

It  is  urgently  desired  that  every  roentgenologist  to  whom 
this  apparatus  is  delivered  take  the  time  necessary  to  study 
it  over  and  to  acquire,  at  least  initially,  the  point  of  view  of 
the  designer.  Simply  because  some  particular  feature  with 
which  he  has  been  familiar,  and  which  has  been  more  or 
less  fashionable  among  roentgenologists,  is  missing,  is  not 
a  sufficient  excuse  for  general  condemnation  or  rejection 
of  the  standard  outfit.  After  making  sure  that  the  appara- 
tus is  properly  assembled  every  operator  should  go  rapidly 
through  the  steps  in  handling  it  with  a  view  to  smoother 
operation  and  to  saving  time.  The  instructions  which  are 
given  may  serve  as  a  basis  for  such  self-drill,  and  it  is  of 
course  to  be  expected  that  many  modifications  of  procedure 
and  inexpensive  additions  to  equipment  may  readily  be 
provided  on  the  initiative  of  the  operating  roentgenologist. 

Every  roentgenologist  is  advised  to  file  and  retain  all 
copies  of  instructions  and  catalogues  or  blue  prints  fur- 

149 


150 


U.  S.  ARMY  X-RAY  MANUAL 


nished  with  the  outfit  by  the  manufacturer.  These  may- 
be of  considerable  assistance  in  case  of  breakdown  or 
damage,  even  though  the  directions,  in  some  measure,  do 
not  correspond  with  the  general  instructions  given  in  this 
manual. 


Fig.  62.     Standard  U.  S.  Army  x-ray  table  with  insulating  masts 
and  holders  and  box  for  standard  type  tube. 


Army  X-Ray  Table. — The  standard  x-ray  table  consists 
of  the  following  principal  parts:     (Figs.  62  and  63.) 

1.  Two  aluminum  end  castings. 

2.  Three  steel  side  rails. 

3.  A  rectangular  frame  as  a  tube-box  cradle. 

4.  A  lead-covered  tube  box. 

5.  A  special  detachable  shutter. 


NEW  APPARATUS  151 

6.  A  rectangular  wooden  frame  supporting  a  stretcher 
type  top. 

7.  An  operating  switch. 

8.  A  special  screen  carrier. 

9.  High  tension  vertical  insulators. 

10.     A  tube  holder  for  working  above  the  table. 


Fig.  63.  Standard  U.  S.  Army  x-ray  table  complete  with  box  for 
radiator  type  tube. 

When  the  table  is  to  be  used  with  the  portable  outfit  a 
tube  box  designed  for  the  radiator  type  of  tube  must  be 
used.  For  the  usual  base  hospital  outfit,  a  tube  box  taking 
the  standard  tubes  is  supplied.  In  the  former  the  high 
tension  insulators  both  enter  the  same  end  of  the  box,  in 
the  latter  they  enter  at  opposite  ends.  Any  or  all  of  num- 
bers 8,  9,  and  10  may  be  omitted  in  special  cases. 


152 


U.  S.  AR]\IY  X-RAY  MANUAL 


In  the  description  following,  numbers  in  parenthesis 
refer  to  the  figures  in  the  text,  not  to  manufacturers'  stock 
or  replacement  numbers. 

End  Castings. —  (Fig.  64)  The  end  castings  (41)  have 
four  slots  (42)  on  each  side.  These  take  the  ends  of 
the  steel  side  rails.  Two  rails  (45)  are  used  on  the  opera- 
tor's side  of  the  table  and  one  on  the  other  side.  When 
using  the  regular  top  the  rails  should  be  placed  in  the 


Fig.  64.     Framework  of  standard  army  x-ray  table  and  operating 
pull  switch  (49). 


upper  of  each  pair  of  slots.  If  one  must  use  an  army  lit- 
ter, use  the  lower  slots.  Holes  are  provided  to  mount  the 
masts  for  overhead  work. 

Rails. —  (Fig.  64)  The  round  rails  have  tightening" 
screws  (48)  with  permanently  attached  handles.  Sliding 
on  one  of  these  rails  are  three  rings  (46,  85,  95).  The  one 
at  the  left  serves  to  lock  the  screen  carriage,  the  center  one 
locks  the  tube  box  against  longitudinal  run  and  also  may  be 
used  to  secure  a  tube  shift  of  either  10  or  15  centimeters. 
The  right-hand  ring  serves  in  measuring  any  desired  tube 


NEW  APPAKATUS 


153 


shift.     These  should  always  be  placed  on  the  rail  in  the 
order  shown. 

Cradle. —  (Fig.  65)  The  cradle  has  three  roller-bear- 
ing wheels  (81)  to  give  longitudinal  run  on  the  side 
rails.  The  single  roller  on  the  right  has  a  screw  brake 
to  be  used  when  lifting  the  box.     The  cross  piece  on  the 


Fig.  65.    Details  of  tube  box,  cradle  and  shutter^  standard  army 
x-ray  table. 


operator's  side  carries  a  tube  box  brake  (57)  for  lateral 
locking  when  in  use,  also  three  stops  for  tube  shift  meas- 
urement. The  one  near  the  center  (84)  is  permanently 
attached,  as  is  also  the  one  at  the  right  (82).  The  third 
(83)  is  placed  close  to  the  roller  and  when  the  ring  (85) 
is  placed  between  (83)  and  (84)  we  have  a  15  cm.  shift; 
by  changing  the  position  of  the  screw  (57)  of  the  cross 
run  brake,  we  may  secure  a  10  cm.  shift  between  stop  (84) 
and  the  stop   (80)   on  the  brake. 


154 


U.  S.  ARMY  X-RAY  MANUAL 


Box. — (Figs.  65,  66  and  67)  Two  types  of  box  are 
built,  one  for  use  with  the  radiator  type  Coolidge  tube,  the 
other  for  the  ordinary  tubes.  The  former  must  he  used  on 
all  portable  outfits,  the  latter  is  known  as  the  base  hospital 
tube  box.  In  the  portable  box  both  insulators  enter  at 
one  end.    In  the  base  hospital  one  is  placed  at  each  end. 

In  both  boxes  the  tube  mount  slides  into  the  box  at  the 


Fig.  66.     Mounting  of  standard  type  tube  in  army  x-ray  table. 


end.  Fig.  67  shows  the  mounting  with  insulators  for  the 
radiator  type  of  tube.  The  partition  (62-63)  is  covered 
with  lead  rubber  and  the  upper  portion  is  removable  for 
insertion  of  the  tube.  The  tube  may  be  raised  or  lowered 
or  shifted  longitudinally  for  centering.  The  insulating 
posts  with  the  transverse  wire  (69)  are  used  in  adjusting 
the  target  position.  All  connections  to  the  tube  are  to  be 
made  before  inserting  the  slide  in  the  box. 

Shutter. —  (Fig.    65)    The    shutter    has    double    slides; 


NEW  APPARATUS 


155 


one  pair  controlled  by  the  outer  knob  (74)  gives  a  dia- 
mond-shaped opening;  that  controlled  by  the  inner  knob 
(75)  gives  a  slit  parallel  to  the  length  of  the  table.  The 
shutter  is  attached  to  the  box  by  the  pins  (56)  and  clamps 
(71),  as  shown,  and  these  must  be  closed  before  using. 


Fig.  67.     Tube  box  and  mount  for  radiator  type  tube,   standard 
army  x-ray  table. 


Top. —  (Fig.  64)  The  rectangular  frame  (30)  is  nar- 
rower than  the  supporting  ends  of  the  table,  permitting  a 
slight  lateral  shift  of  the  patient  without  disturbing  him 
on  the  stretcher.  A  raised  ridge  projects  on  one  side  to 
engage  a  groove  in  the  stretcher  type  of  top.  This  allows 
a  certain  amount  of  longitudinal  shift.  A  little  paraffin 
as  a  lubricant  on  the  ridge  will  serve  to  make  the  top 
move  readily,  even  with  a  heavy  patient. 


156 


U.  S.  ARMY  X-RAY  MANUAL 


Fig.  68.     Screen-carrying     mechanism,     complete     standard     army 
x-ray  table. 


NEW  APPARATUS  157 

Switch. —  (Fig.  64)  When  using  the  "Delco"  engine 
to  operate  the  portable  outfit  the  switch  may  open  and 
close  two  circuits ;  in  this  case  the  usual  foot  switch  cannot 
he  used.  A  special  pull  switch  (49)  operated  by  a  string 
running  along  the  rail  is  supplied. 

Screen  Support. —  (Fig.  68)  The  screen  support  was 
designed  to  enable  the  screen  to  be  carried  to  any  working 
position  parallel  to  the  table  top  without  having  any  por- 
tion obstructing  the  work  of  the  operator.  For  localization 
work  it  may  be  locked  in  any  desired  position. 

It  has  the  following  features : 

1.  It  runs  freely  on  the  two  side  rails. 

2.  It  is  counterbalanced  so  as  to  run  up  and  down  with 
ease. 

3.  It  may  be  rotated  about  two  vertical  axes,  enabling 
the  pierced  center  of  the  screen  to  be  brought  easily 
into  position. 

4.  It  may  be  locked  against  each  motion  separately. 

5.  It  may  be  locked  as  to  up  and  down  motion  and  yet 
rotate. 

6.  The  screen  may  be  inclined  if  need  arises.  The  car- 
rier is  mounted  in  a  tube  (91)  with  bearings  running 
on  the  lower  rail,  and  three  rollers  (93)  on  a  verti- 
cal axis  hold  it  in  line  on  the  upper  rail.  (96)  is  a 
heavy  tube  fitting  into  (91)  and  turns  on  a  cone 
bearing  at  the  base.  (109)  is  an  adjustable  rod  to 
which  is  attached  the  screen  clamp  (106).  (98)  is 
the  clamp  for  vertical  motion;  (95)  for  longitudinal 
run;  (94)  for  rotation  in  the  tube;  (106)  for  rota- 
tion about  the  corner  of  the  screen. 

Vertical  Insulators. —  (Fig.  62)  The  special  insulat- 
ing masts  may  be  used  as  follows : 

1.  In  base  hospital  work  with  an  overhead  wiring  sys- 
tem they  serve  to  connect  to  the  tube  box.    They  are 


158  U.  S.  ARMY  X-RAY  MANUAL 

then  placed,  one  at  each  end  on  the  operator's  side 
of  the  table. 
2.  To  connect  the  portable  instrument  box  for  work 
with  tube  above  the  table.  They  are  then  placed 
both  at  one  end  of  the  table.  Two  extra  reels  and  a 
tube  holder  are  needed  for  this  arrangement. 
Setting  Up  Table  (Portable)— 

1.  Unpack  all  of  outfit  and  check  list  to  ensure  that  no 
parts  are  mislaid. 

2.  Decide  on  position  for  table  and  instrument  box, 
and  which  shall  be  the  operating  side  of  table. 

3.  Lay  two  rods  (45)  down  on  side  to  be  used  by  the 
x-ray  operator;  one  of  these  must  have  locking  and 
stop  rings. 

4.  Place  end  frames  (41)  in  position  and  drop  rods  into 
notches.  Use  all  upper  notches  unless  army  litter  is 
to  be  used. 

5.  Place  screen  roller  carriage  (91)  in  position  and 
tighten  end  screws  on  all  rods.  Run  (91)  to  left 
of  operator's  position. 

6.  Hook  cradle  under  rollers  on  tube  box  with  the  two 
roller  ends  of  cradle  on  the  operator's  side  of  the 
table.  Lock  cross  brake  (51)  and  set  cradle  on  rails, 
then  release  brake  (51).  Attach  working  cross  lock 
and  be  sure  it  is  in  proper  position.     See  Fig.  65. 

7.  Attach  diaphragm  (70)  to  box  and  lock  in  position. 

8.  Set  (96)  into  (91),  then  attach  screen  and  clamp 
with  screw  (103). 

9.  Unlock  (98)  and  put  on  enough  small  weights  to 
counterbalance  the  screen. 

10.  Attach  pull  switch  to  the  end  of  table  toward  instru- 
ment box. 

11.  Pull  out  drawer  from  tube  box  and  place  on  a  good 
support. 


NEW  APPARATUS  159 

12.  Remove  cover  of  inner  box  of  tube  shipping  case  by 
unhooking  the  hasps  at  each  end,  and  raise  the  cor- 
ner by  grasping  each  hasp. 

13.  Place  the  tube  in  position  shown  in  Fig.  67.  Make 
the  cathode  connection  by  turning  the  tube  in  the 
holder  before  tightening.  Then,  approximately  cen- 
ter and  tighten  holder.  Connect  to  the  radiator  by 
means  of  a  short  piece  of  wire.  Do  not  use  screw 
as  a  binding  post. 

14.  Place  rectangular  frame  (30)  with  ridge  away  from 
operator. 

Note, — Be  sure  to  retain  the  box  intact  in  which  the 
tube  is  shipped,  and  in  case  of  reshipment  proceed  as 
follows : 

To  pack  the  tube,  place  it  in  the  inner  box  so  that  the 
radiator  is  i/4  inch  from  the  end  of  the  box. 

Place  cover  of  inner  box  in  position. 

Press  cover  down  carefully  and  close  spring  hasps,  being 
absolutely  sure  that  the  hasp  is  hooked. 

After  closing  cover  of  outer  box,  fasten  down  by  means 
of  the  hasp  provided  for  that  purpose. 
Cautions — 

1.  Do  not  bend,  bruise  or  jamb  parts. 

2.  Do  not  remove  screen  without  first  locking  (98),  as 
counter  weight  may  cause  damage. 

3.  Do  not  turn  screws  so  tight  that  threads  are  stripped. 

4.  Do  not  fail  to  set  cross  run  brake  (51)  before  lifting 
tube  box  off  or  on. 

5.  If  the  supporting  side  rails  are  slightly  bent  the 
tube  carriage  will  run  hard  or  bind.  Place  box  in 
the  middle  of  the  run  and,  loosening  the  end  nuts, 
(48)  rotate  upper  rods  about  their  own  axes  until 
the  single  back  roller  is  free  on  both  sides,  i.  e.,  does 
not  rub  on  its  support. 


160  U.  S.  ARMY  X-RAY  MANUAL 

6.  Always  remove  screen  from  its  holder  before  remov- 
ing screen  carriage. 

7.  Note  the  cone  bearing  on  the  lower  end  of  the  car- 
rier post.  Do  not  stand  the  carrier  on  this,  as  it  may 
easily  be  roughened. 

8.  If  the  screen  carrier  does  not  run  freely  or  is  too 
loose  at  the  top,  the  eccentric  mounting  on  the  in- 
side of  the  roller  bearing  should  be  loosened  and  ad- 
justed so  that  there  is  very  little  play  between  these 
rollers  and  the  rail.  If  tightened  in  this  position 
the  carrier  will  run  freely. 

Also,  note  that  the  ring  (95)  has  a  hole  90°  from  the 
handle  into  which  a  small  thumb  nut  projects,  making  the 
attachment  with  the  movable  carrier;  while  (85)  has  a 
projection  intended  to  engage  a  slot  on  the  under  side  of 
the  cross  piece  of  the  cradle,  to  serve  as  a  lock  for  longitudi- 
nal run  of  tube  box. 

Some  Operating  Points. — After  the  table  is  set  up  and 
made  reasonably  level  and  all  adjustments  have  been  made, 
it  is  strongly  advised  that  the  operator  practice  manipula- 
tion until  he  can  instinctively  and  certainly  grasp  the 
locking  devices  whenever  necessary  for  his  work. 

There  are,  then,  six  knobs  to  be  operated,  three  con- 
trolling the  screen  carrier  and  three  the  tube  box  and  dia- 
phragm. 

Number  106  will  usually  be  set  according  to  the  opera- 
tor's idea  of  using  the  screen  and  need  not  generally  be 
unlocked. 

It  is  expected  that  the  operator  will  stand  between  the 
screen  carrier  and  the  diaphragm  control,  using  the  right 
hand  to  control  the  screen  box  and  its  locks.  It  may  be 
suggested  that  if  the  operator  will  acquire  the  habit  of 
grasping  the  rod  (109)  in  order  to  control  the  screen 
position,  the  left  hand  need  never  be  in  the  radiation,  and 


NEW  APPARATUS  161 

the  right  hand  can  remain  free  to  control  shutters  and 
rail  lock,  Fig.  69.     A  little  time  spent  in  adjusting  one's 


Fig.  69.     Method  of  handling  screen  and  shutter  on  all  standard 
army  x-ray  tables.     Litter  top  removed. 

motions  and  ideas  to  those  that  prevailed  when  the  ap- 
paratus was  designed  will  greatly  expedite  its  accurate  use. 


162 


U.  S.  ARMY  X-RAY  MANUAL 


List  of  Numbers  Referring  to  Illustrations  of  Stand- 
ard Tables 

Numbers  refer  to  the  illustrations  and  not  to  manufac- 
turers' stock  or  replacement  numbers. 


PART.  NO. 

Top 

Rectangular   frame  30 

Bakelite  stretcher  31 

Frame 

End  frames  41 

End  frame  slots  42 

Holes  for  mast  support  43 

Rods   (side  rails)  45 

Ring  stop  46 

Screw   handles   on   rods  48 

Switch  49 

Tube  Box 

Roller  with  cross  run  lock       51 

Rollers  without  lock  52 

Aluminum  window  54 

Ventilation  opening  55 

Register  pins   for  shutter  56 

Lock,  cross  run  57 

Partition    (lower   half)  62 

Partition  (upper  half)  63 

Insulator  (cathode)  64 

Insulator   (anode)  65 

Binding  Posts  66 

Tube  support  posts  67 

Tube  clamp  68 

Tube  centering  wire  69 

Shutter 

Shutter  complete  70 

Shutter  clamps  71 
Screen  carrier  connecting  post    72 

Diaphragm    opening  73 

Diamond-opening    control  74 

Slit-opening  control  75 


PART.  NO. 

Tube  Box  Cradle 
Stop  position  for  10  cm.  shift    80 

Rollers  81 

Stop  for  variable  shift  82 

Stop  for  15  cm.  shift  83 

Stop  84 

Lock  to  rail  85 

Screen  Carrier 

Socket  bearing    _  91 

Lower    rail    carriage    frame  92 

Upper  rail   bearing   rolls  93 

Clamp  against  rotation  94 
Clamp  against  longitudinal 

run  95 

Main  post  96 

Sliding  sleeve             ^  ^  97 

Clamp   (vertical  position)  98 

Pulley  99 

Wire  cord  100 

Balance  weights  101 

Socket  for  horizontal  arm  102 

Clamps  (screw)  103 

Screen  holder  frame  104 

Screen  holder  latch  105 

Screen  clamp  106 

Knobs  to  lift  screen  107 

Screen  108 

Rod  to  screen  frame  109 


Additional    High    Tension 
Insulators 

Vertical  masts  21 

Frame  for  supporting  masts      22 
Short  insulator   for  keeping 
high    tension    wires    away 
from  frame  23 


NEW  APPARATUS  163 

Fluoroscopic  Room  Illumination. — It  is  strongly  urged 
that  the  lighting  of  fiuoroscopic  rooms  be  properly  ar- 
ranged. One  should  have  a  dim  light  for  use  in  placing 
patients,  etc.,  and  no  light  when  fluoroscoping.  The  port- 
able outfit  provides  for  operating  the  needed  light  from  the 
Delco  generator.  When  the  operating  switch  is  closed  the 
lights  go  out,  and  on  opening  this  switch  they  are  automat- 
ically  lighted.  It  is  advised  that  a  ruby  lamp  be  used  in- 
tended for  operation  on  a  circuit  above  110  volts.  The 
connection  used  with  the  portable  unit  is  shown  in  Fig.  76 
and  a  similar  connection  can  be  made  for  other  outfits. 

To  Find  Target-Screen  Distance.— On  the  standard 
army  x-ray  tables  the  following  method  will  serve  to  meas- 
ure the  distance  from  target  to  screen: 

The  upright  support  U  fits  in  the  tube  Q,  Fig.  70  and  the 
screen  carrier  is  fastened  to  the  sliding  sleeve  R.  The  dis- 
tance from  the  top  of  the  tubing  Q  to  the  under  side  of  R 
is  related  to  the  target-screen  distance  F^S  as  shown,  F^S 
=  n-\-d  -j-  I  where  n  and  I  are  fixed  lengths.  Hence  if  one 
target-screen  distance  is  found,  w  +  Z  can  at  once  be  de- 
termined. 

Put  the  cross  wire  marker  on  the  table  in  the  vertical 
ray.  Shift  the  tube  by  use  of  the  table  stops  an  exact 
distance,  say  10  or  15  cm.,  and  adjust  the  screen  up  or 
down  until  the  image  shift  and  tube  shift  are  equal.  Then 
the  target-screen  distance  is  twice  the  distance  between 
screen  and  cross  wire  marker. 

Measure  the  distance  BX  and  subtract  this  from  the 
length  so  found,  and  the  difference  is  I  -\-  n.  Record  this 
on  a  shipping  tag  and  attach  to  the  table.  Thereafter,  if 
the  target-screen  distance  is  required,  measure  BX  and  add 
I  -^  n  as  recorded. 

To  check  your  measurement  lay  a  strip  of  metal  about 
four  inches  long  on  the  table.     Raise  the  screen  until  the 


164 


U.  S.  ARMY  X-RAY  MANUAL 


shadow  becomes  twice  the  length  of  the  strip.     Measure 
screen-object  distance  and  double  the  result  for  FS. 


^ 


W^ 


.a 


Screen 

I  I 


7Z 


£ 


Fig.  70.     Measurement  of  target-screen  distance,   standard  screen 
carrier. 


Examples — 

1.  Using  a  10  cm.  tube  shift  and  setting  the  sliders  of 
method  A  10  cm.  apart,  a  piece  of  lead  was  placed  on  the 
table  and  its  edge  so  placed  that  its  shadow  coincided  with 
one  of  the  metal  edges  of  the  marker ;  shifting  the  tube  10 
cm.,  the  screen  was  raised  until  the  shadow  of  the  lead 


NEW  APPARATUS  165 

coincided  with  the  other  marker.  The  object-screen  distance 
was  then  38.7  cm.  The  target-screen  distance  was  then 
38.7  X  2  =  77.4. 

2.  With  length  of  shadow  double  that  of  the  object,  the 
actual  distance  between  screen  and  the  object  was  39  cm. 
Double  this,  or  78  cm.,  equals  the  distance  between  the 
plane  of  the  screen  and  the  plane  of  the  focal  spot  of  the 
target. 

78  cm.  =  total  distance  screen  to  target 
45  cm.  =  variable  distance 


33  cm.  =  the  distance  that  the  sliding  or  adjustable 
piece  on  the  upright  arm  of  the  wall  meter 
is  to  be  raised  and  set  above  the  brass  lug 
on  the  lower  right. 

Centering  Tube  in  the  Box  Beneath  the  Table. — It  is 

desirable  that  the  focal  spot  of  the  target  should  be  verti- 
cally below  the  center  of  the  diaphragm  in  the  various 
methods  of  localization.  In  order  to  determine  whether  this 
is  the  case,  proceed  as  follows : 

1.  Close  up  the  diamond-shaped  opening  of  the  shutter 
to  about  %  inch. 

2.  Lock  the  tube  box  in  position  and  bring  the  opening 
of  the  screen  so  that  the  illumination  shows  symmetrically 
thereon. 

3.  Suspend  a  small  metal  ball,  B,  by  a  string  passing 
through  the  center  of  the  opening,  and  observe  when  this 
ball  comes  to  rest  whether  its  shadow  falls  symmetrically 
upon  the  projection  of  the  diaphragm.  If  not,  or  if  on 
narrowing  the  diaphragm  still  further,  the  narrow  beam 
of  rays  passes  by  the  ball  so  that  it  does  not  cast  a  shadow 
on  the  small  illuminated  area  of  the  screen,  it  is  evident 


166 


U.  S.  ARMY  X-RAY  MANUAL 


that  the  tube  is  not  properly  centered,  and  the  position 
of  the  shadow  also  gives  ?ai  indication  of  the  direction  of 
tube  movement  require.    Fig.  71. 

An  approximate  idea  of  whether  the  tube  is  properly 
centered  or  not  may  be  gained  by  bringing  the  perforation 
in  the  center  of  the  screen  to  the  center  of  the  projection 
of  the  small  diagonal  opening  of  the  shutter.    "When  the 


"Phmb  Line 


N 


V     I 


Screen 


Screen 


Vlumb  Line 


Vertical  Fai 


I Ytrtical  Jfay 


■<>' 


Shutter 


Shutter 
Sliqhtlj  opened 


Fig.  71.  (a)  Correct  position  of  shadow  of  plumb  bob.  Tube 
properly  centered. 

(b)  Projection  of  plumb  bob  on  fluorescent  screen,  incorrect  posi- 
tion. 

screen  is  down  close  to  the  table  with  the  carrier  locked 
against  longitudinal  motion  and  against  rotation,  raise  the 
screen  by  the  vertical  movement  of  the  carrier  and  see 
whether  it  retains  its  symmetrical  position.  An  idea  of  the 
amount  by  which  the  tube  needs  to  be  shifted  may  be  ob- 
tained in  this  way. 

It  is  also  suggested  that,  if  the  tube  needs  to  be  moved  in 
the  direction  in  which  the  holder  slides  out  of  the  box, 
one  can  slide  the  holder  itself  out  and  test  for  correctness, 


NEW  APPARATUS 


167 


measure  the  distance,  and  finally  shift  the  tube  the  same 
amount. 

The  U.  S.  Army  Portable  X-Ray  Unit. — By  the  coopera- 
tion of  various  manufacturers  a  semi-portable  outfit  has 
been  developed  which  may  be  used  in  mobile  units.  The 
unit  is  shown  in  Fig.  72  and  diagramatically  in  Fig.  73. 

The  important  features  of  the  outfit  are  the  portable 
power  plant,   the   self-rectifying   Coolidge   tube,   and  the 


Fig.  72.     United  States  Army  portable  x-ray  unit  complete. 


special  table.  Having  the  complete  generating  equipment, 
it  is  admirably  adapted  to  service  in  strange  territory 
where  the  electrical  supply  is  not  suitable  for  standard  ma- 
chines or  is  likely  to  fail  because  of  war  conditions. 

The  gasoline  engine  is  direct-connected  to  a  generator 
which  supplies  power  for  the  x-ray  and  filament  trans- 
formers (a.c.)  and  a  small  amount  of  current  (d.c.)  for 
the  control  circuit.  The  primary  circuit  requires  no  con- 
trol resistance,  regulation  for  the  two  working  settings 
being  made  by  shifting  the  throttle  by  means  of  the  d.-c. 


168 


U.  S.  ARIVIY  X-RAY  MANUAL 


XRflY  TUBE 


FiLRM£NT 
TnmSFORMER 


THRNSFORMER 


BLflCA 


Fig.  73.  Wiring  diagram  for  United  States  Army  portable  x-ray 
unit.  Dotted  lines  show  connections  for  those  machines  having  spe- 
cial control.    In  other  cases  these  wires  are  omitted. 


NEW  APPARATUS  169 

control  circuit,  changing  the  speed  and  thereby  the  voltage 
of  the  generator.  The  secondary  circuit  contains  no  rec- 
tifying device  since  the  tube  allows  only  each  alternate  half 
wave  to  pass.     (See  page  36  for  a  description  of  the  tube.) 

Fluoroscopic  work  is  done  at  5  ma.  and  all  radiographic 
work  at  10  ma.  The  maximum  operating  gap  is  about  5 
inches,  but  may  be  reduced  if  desired  by  control  of  the 
machine  speed. 

Owing  to  the  drop  in  line  voltage  upon  closing  the  operat- 
ing switch,  it  is  necessary  to  secure  a  uniform  filament  cur- 
rent by  inserting  a  "booster"  in  the  primary  circuits  of 
the  two  transformers.  This  is  merely  a  small  transformer, 
which  by  carrying  the  main  transformer  primary  current 
adds  enough  voltage  to  the  filament  transformer  primary 
to  compensate  for  the  drop  of  voltage  in  the  line. 

Engine.* — The  engine  must  be  firmly  fastened  to  a  solid 
base  by  means  of  lag  bolts  or  by  some  other  convenient 
method.  All  fuel  must  be  strained  when  filling  tank,  as 
impurities  of  any  kind  are  certain  to  clog  fuel  pipes. 

Use  a  good  grade  of  medium  oil  and  always  make  sure 
that  the  crank  case  is  well  filled  before  starting  engine. 

To  start  the  engine,  turn  the  fly-wheel  rapidly  by  means 
of  the  crank,  immediately  remove  crank  and  then  press 
starting  button  and  cut  off  air  by  means  of  lever  on  mixing 
valve  body.  When  the  engine  has  run  for  a  few  seconds, 
advance  air  adjustment  lever  to  the  point  where  the 
engine  runs  regularly  and  witb  the  leanest  possible  mixture. 
A  little  practice  will  enable  the  operator  to  do  this  very 
quickly.  This  adjustment  will  vary  with  climatic  condi- 
tions and  the  kind  and  grade  of  fuel  used.  It  will  be 
found  to  be  slightly  different  when  the  engine  has  warmed 
up  from  what  it  was  when  the  engine  was  started. 

♦See  also  "Delco"  circular  on  model  9011,  furnished  by  the  manu- 
facturer. 


170  U.  S.  ARMY  X-RAY  MANUAL 

If  the  engine  does  not  start,  a  few  simple  tests  may 
determine  the  cause.  Go  carefully  over  all  wiring  and  be 
sure  that  all  electrical  connections  are  tight  and  clean. 
Test  to  make  sure  that  starting  battery  is  not  exhausted. 

Examine  the  spark  plug  carefully  and  if  the  porcelain  is 
broken  or  cracked,  replace  plug  with  a  new  one  if  possible. 
Hold  the  spark  plug  connecter  about  Yg  inch  away  from 
spark  plug  terminal  and  turn  fly-wheel  over  several  times 
by  means  of  the  crank  and  see  if  a  good  spark  is  obtained 
in  this  manner.  If  not,  the  plug  may  be  greasy  or  dirty; 
remove  and  clean  thoroughly  with  gasoline  and  adjust 
the  distance  between  the  points  to  about  1/32  of  an  inch, 
or  until  a  dime  can  be  just  passed  between  them. 

Next,  look  at  timer  contacts  to  see  that  they  are  properly 
adjusted  and  are  making  good  contact  every  time  they  close. 
If  necessary,  clean  these  contacts  with  a  piece  of  fine  sand 
paper.  To  adjust  the  distance  between  the  points  turn  the 
engine  over  until  the  points  open  to  their  full  extent.  In 
this  position  a  dime  should  just  slip  between  the  points. 
If  necessary,  adjust  them  by  turning  the  contact  screw  in 
or  out  until  the  proper  distance  is  obtained. 

Next,  examine  commutator  and  brushes.  The  commuta- 
tor may  be  dirty  or  greasy.  It  should  never  be  allowed  to 
remain  in  this  condition,  if  the  generator  is  to  operate  at 
maximum  efficiency.  Hold  a  piece  of  clean  cloth  soaked 
in  a  little  kerosene  against  the  commutator  while  the  engine 
is  running.  Never  use  oil  other  than  kerosene  on  com- 
mutator and  always  wipe  dry  with  a  piece  of  clean  cloth 
afterwards.  Examine  brushes  to  see  that  they  are  in  good 
condition  and  are  making  good  contact. 

To  test  your  fuel  line,  fill  the  priming  cup  from  a  small 
oil  can  with  gasoline,  and  crank.  If  the  engine  will  run 
when  using  gasoline  from  the  can,  and  will  not  run  other- 


NEW  APPARATUS  171 

wise,  it  indicates  that  fuel  connections  are  loose  or  that 
the  fuel  hole  in  mixing  valve  body  is  clogged.  Be  sure 
there  is  no  water  in  the  gasoline  tank.  The  fuel  hole  in 
mixing  valve  body  or  line  may  be  cleaned  out  by  blowing 
through  it  or  by  means  of  a  fine  wire.  These  few  tests 
will  usually  locate  the  trouble.  Now  look  at  the  cable  leads 
which  are  all  stamped  with  a  corresponding  number  on  the 
engine  switch  board.  Be  sure  that  they  are  properly  con- 
nected to  both  engine  and  transformer  unit.  The  amount 
of  gasoline  on  continuous  fluoroscopic  work  will  be  about  1 
gallon  per  hour.  On  intermittent  work,  as  is  usually  the 
actual  case,  a  gallon  will  last  about  31/2  hours. 

Note. — It  may  be  noted  that  the  wiring  diagram  as  in- 
dicated for  the  portable  unit  has  three  wires  to  the  voltage 
control,  and  that  the  x-ray  switch  has  to  open  and  close  a 
circuit,  on  the  left,  through  this  coil  and,  on  the  right, 
through  the  x-ray  transformer.  This  arrangement  was 
made  in  order  to  speed  up  the  engine  promptly  when  put 
under  load,  but  it  has  been  found  unnecessary.  In  some 
of  the  earlier  machines,  and  perhaps  in  the  later  ones,  this 
connection  may  be  absent.  When  this  is  the  case  the  wiring 
will  be  somewhat  simpler,  since  the  number  of  connections 
will  be  reduced  and  a  slight  change  of  design  of  the  box 
may  be  possible. 

The  Transformer  Unit. — The  x-ray  transformer  unit 
contains  the  apparatus  needed  to  transform  and  control  the 
currents  necessary  for  energizing  the  radiator  type  Coolidge 
tube  used  with  these  outfits.  It  consists  of  the  following 
parts:   (Figs.  74  and  75.) 

The  x-ray  transformer  (1)  transforms  the  low  tension 
alternating  current  from  the  gasoline  engine  generator 
unit  into  suitable  high  tension  current. 

The  filament  transformer  (2)  supplies  the  low  tension 
current  for  heating  the  filament  of  the  x-ray  tube. 


172 


U.  S.  ARMY  X-RAY  MANUAL 


The  booster  transformer  (3)  keeps  the  filament  of  the 
x-ray  tube  constant. 

The  filament  control   (4)   varies  the  amonnt  of  current 


Fig.  74.     Instrument  box  for  portable  unit,  front  view. 

passing  through  the  x-ray  tube.  A  small  knob  will  be 
found  projecting  from  the  side  of  this  regulator — this  is 
to  open  and  close  the  circuit  through  the  primary  of  the 


NEW  APPARATUS  173 

filament  transformer.  When  pushed  in  it  is  closed,  as  it 
should  ordinarily  remain. 

The  engine  rheostat  (5)  serves  as  a  means  for  controlling 
the  speed  of  the  gasoline  engine.  Moving  the  contact  to- 
ward the  front  of  the  box  increases  the  speed  of  the  engine 
and  thus  raises  the  voltage  of  the  generator. 

The  x-ray  switch  (6)  opens  or  closes  the  circuit  to  the 
primary  of  the  x-ray  transformer  and  to  the  auxiliary  throt- 
tle control. 

The  voltmeter  (7)  measures  the  voltage  of  the  generator. 

The  milliammeter  (8)  measures  the  amount  of  current 
passing  through  the  x-ray  tube. 

The  main  terminal  board  (9),  whose  five  terminals  pro- 
ject from  rear  side  of  the  case,  provides  a  means  for  con- 
necting the  x-ray  transformer  unit  to  the  gasoline  engine 
generator  unit  by  means  of  the  cable. 

The  pull  switch  terminal  board  (10)  is,  as  the  name  indi- 
cates, for  the  purpose  of  attaching  a  pull  switch  to  the 
apparatus.  The  split  lugs  at  the  end  of  the  switch  cable 
are  to  be  inserted  into  the  sockets  in  this  terminal  board 
to  connect  the  pull  switch  in  circuit.  These  connections  put 
the  pull  switch  in  parallel  with  the  x-ray  switch  and  per- 
mit the  closure  of  the  circuit  by  either  independent  of  the 
other. 

After  the  engine  and  x-ray  table  are  set  up,  place  the 
x-ray  transformer  unit  in  position,  close  to  the  end  of  the 
table  and  so  that  the  high  tension  outlets  are  equally 
spaced  between  the  legs  of  the  table.  This  is  very  im- 
portant and  should  not  be  forgotten. 

Unlock  the  box,  raise  the  lid  to  an  angle  of  about  45° 
from  horizontal,  and  slide  the  cover  of  the  box  slowly  to 
the  left  until  the  two  hinge  sections  have  been  disengaged 
one  from  the  other.  The  cover  can  now  be  removed  from 
the  box. 


174 


U.  S.  ARMY  X-RAY  MANUAL 


Pull  out  the  two  door  bolts.  The  door  in  front  can  now 
be  let  down  so  that  work  can  be  done  readily  in  the  in- 
terior of  the  box.  This  door  should  be  kept  open  at  all 
times  when  the  unit  is  in  operation  to  avoid  damage  by 
corona,  etc. 

Push  the  split  terminal  lugs  at  one  end  of  the  cable  into 


Fig.  75.     Instrument  box  for  portable  unit  showing  instruments, 
high  tension  terminals,  and  openings  for  connections. 

the  sockets  on  main  terminal  board.  These  lugs  are  of  dif- 
ferent sizes  so  that  they  will  only  fit  one  way  in  the  termi- 
nal board,  and  no  mistake  should  be  made.  Connect  the 
numbered  lugs  at  the  other  end  of  the  cable  to  the  corre- 
spondingly marked  connection  posts  on  the  switch  board 
of  the  engine.  Connect  pull  switch,  if  one  is  to  be  used,  by 
inserting  the  split  lugs  on  the  switch  cable  in  the  sockets 
in  the  pull  switch  terminal  board. 

The  high  tension  terminals  (11)  and  (12)  will  be  found 


NEW  APPARATUS  175 

held  in  place  in  the  cover  by  means  of  a  clamp  device. 
These  terminals  should  be  removed  and  screwed  into  the 
sockets. 

These  sockets  and  terminals-  are  provided  with  different 
sized  threads  at  their  ends  so  that  the  terminals  can  only 
fit  into  their  proper  socket.  The  high  tension  terminal  (11), 
provided  with  the  spring  hook  terminal,  screws  into  the 
single  socket.  The  remaining  terminals  (12)  can  be  screwed 
one  into   each   of  the  remaining  sockets. 

Attach  the  cord  from  the  positive  terminal  to  the  posi- 
tive terminal  of  the  tube  box  and  the  cords  from  the  two 
negative  terminals  to  the  two  binding  posts  on  the  nega- 
tive terminal  of  the  tube  box. 

Open  the  x-ray  switch,  the  pull  switch,  and  the  line 
switch  on  the  board  of  the  engine ;  move  the  sliding  con- 
tact of  the  engine-rheostat  as  close  to  the  hinge  side  of  the 
box  as  it  will  go.  Start  the  engine  and  close  the  switch 
on  the  switch  board  of  that  unit.  The  filament  of  the  tube 
should  now  be  incandescent.  Slowly  move  the  contact  on 
the  engine  rheostat  toward  the  front  of  the  box.  The 
voltmeter  should  indicate  higher  and  higher  voltage.  Con- 
tinue until  the  voltmeter  indicates  about  160  volts. 

For  radiographic  work,  having  adjusted  the  engine 
speed  by  means  of  the  engine  rheostat  until  the  voltmeter 
reads  160  volts,  set  the  filament  control  at  1.9,  close  the 
x-ray  switch  and  readjust  the  engine  rheostat  and  filament 
control  until  the  milliammeter  reads  10  ma.,  when  the  volt- 
meter should  read  from  110  to  115  volts. 

Now  open  x-ray  switch  and  read  the  voltage  generated 
at  no  load,  leaving  the  rheostat  set  in  the  10  ma.  position. 
Hereafter,  whenever  radiographic  work  is  to  be  done,  sim- 
ply adjust  the  engine  rheostat  until  the  voltmeter  indicates 
the  voltage  thus  found. 

To  obtain  the  operating  point  for  fluoroscopic  work,  viz.. 


176  U.  S.  ARMY  X-RAY  MANUAL 

5  ma.  at  from  110  to  115  voltmeter  reading,  reduce  the 
speed  of  the  engine  by  means  of  the  engine  rheostat 
until  the  milliammeter  indicates  5  ma.  Upon  examination 
of  the  voltmeter,  it  will  be  found  to  read  from  110  to 
115  volts.  Open  the  x-ray  switch  and  read  the  voltage  gen- 
erated at  no  load,  leaving  the  engine  rheostat  set  at  5  ma. 
point. 

Hereafter,  whenever  fluoroscopic  work  is  to  be  done,  ad- 
just the  engine  rheostat  until  the  voltmeter  again  reads  the 
voltage  thus  found. 

In  order  to  save  fuel  and  wear  and  tear  on  the  engine, 
it  may  be  advisable  to  run  the  latter  on  reduced  speed, 
except  when  making  a  radiograph,  or  during  a  fluoroscopic 
examination,  or  when  it  is  desirable  to  use  red  room  lamps 
designed  for  this  unit.  For  this  reason  an  adjustable  stop 
is  provided  on  the  engine  rheostat.  This  stop  is  set  to  bring 
the  engine  to  proper  speed  for  the  work  in  hand,  so  that 
during  the  interval  between  making  radiographs  or  fluoro- 
scopic examinations,  the  engine  speed  can  be  reduced  and 
reset  for  the  next  operation  by  merely  running  the  contact 
against  the  adjustable  stop. 

This  x-ray  transformer  unit  should,  as  far  as  possible,  be 
kept  dry  inside  and  out,  and  should  be  kept  covered  with 
a  tarpaulin  when  not  in  use.  Care  should  be  taken  to 
prevent  sudden  jarring  and  rough  handling  generally,  to 
minimize  the  danger  of  putting  meters,  etc.,  out  of  adjust- 
ment. 

The  filament  control  must  be  adjusted  carefully  to  give 
the  proper  current  and  primary  voltage,  and  once  adjusted 
it  will  stay  fixed.  Make  sure  the  filam.ent  is  lighted  be- 
fore throwing  on  power :  this  may  easily  be  forgotten  with 
an  enclosed  tube. 

Should  a  spark  pass  in  the  secondary  circuit  when  the 
operating  switch  is  closed,  it  may  be  due  to  a  temporary 


NEW  APPARATUS 


177 


surge.  Unless  an  ' '  arc ' '  results,  do  not  open  the  operating 
switch.  Keep  secondary  wires  well  apart  and  well  away 
from  other  objects  to  prevent  corona  and  leakage.  It  is 
a  good  plan  to  connect  the  frame  of  the  table  to  any  con- 
venient ''ground." 

Red  Light  for  Fluoroscopic  Room. — The  generator  may 
readily  serve  to  give  the  reduced  red  light  needed  in  fluoro- 
scopic work.    Fig.  76  shows  how  this  is  done ;  and  either  a 


ROOM  LIQHT 


HIGH  TENSION  TO  TUBE 

^\A)/LLIflMM£T£f? 


\—mtm 


i^VWWvVWWWh 


ft 


TRANSFORMER 


BOOSTER 

PRiriRRr 


OPERflTlNq 
~  SWITCH 


LINE 

Fig.  76.     Connections    for    red   lamp    over   the    fluoroscopic   table, 
when  used  with  portable  unit. 


high  voltage  ruby  lamp  or  two  16  candle  power,  110  volt 
ruby  lamps  in  series  are  required.  Do  not  connect  in  ex- 
cept as  shown  and  do  not  attempt  to  load  the  generator  up 
with  additional  lights  or  apparatus.  Pulling  the  string 
switch  alternates  x-ray  excitation  and  darkroom  illumina- 
tion. The  extension  cord  and  light  connect  onto  the  box 
at  13,  Fig.  75. 

Limitations. — This  instrument  will  do  the  work  for 
which  it  is  designed,  but  must  not  be  abused.  Do  not 
use  the  radiator  type  Coolidge  tube  on  large  installations  or 
interrupterless  transformers.  It  is  not  furnished  for  this 
purpose.     It  should  only  be  used  for  radiographs  at  10 


178 


U.  S.  ARMY  X-RAY  MANUAL 


Fig.  77.  United  States  Army  bedside  unit,  complete  for  alternat- 
ing current  operation;  double  throw  switch  to  be  drawn  to  the  right, 
loose  connections  below  for  rotary  converter  in  using  direct  current. 


ma.  for  a  maximum  exposure  not  exceeding  45  sec.  with 
two  minute  intervals  between.  For  fluoroscopic  work  it 
may  be  operated  continuously,  long  enough  for  all  practi- 
cal necessities,  at  5  ma.    Do  not  attempt  to  use  this  tube  at 


NEW  APPARATUS  179 

other  than  these  settings.  Never  attempt  to  operate  the 
tube  without  the  radiator. 

The  U.  S.  Army  Bedside  X-Ray  Unit. — The  unit  shown 
in  Fig.  77  was  designed  to  permit  x-ray  examination  in 
wards  to  be  made  with  a  minimum  of  disturbance  of  the 
patient.  Many  cases  of  fracture  and  other  bone  lesions, 
as  well  as  various  chest  conditions,  need  such  examina- 
tions. Pressure  on  the  main  x-ray  outfit  is  often  reduced 
and  time  saved  by  using  such  a  unit. 

This  unit  consists  of  a  combined  cabinet  and  tube  stand, 
a  radiator  type  Coolidge  tube,  special  lead  glass  shield, 
and  a  transformer  and  control  apparatus.  The  latter  are 
enclosed  in  the  cabinet. 

Transformer. — The  transformer  (1)  is  designed  to 
operate  on  alternating  current  of  any  ordinary  frequency, 
if  properly  connected  for  the  supply  voltage  available. 
Since  the  same  primary  circuit  supplies  power  for  both 
filament  lighting  and  x-ray  operation  only  one  switch  needs 
to  be  opened  or  closed. 

Tube. — The  radiator  type  of  tube  (2)  with  a  special 
molded  lead  glass  shield  is  used  exclusively  on  these  units. 
The  tube  will  operate  continuously  with  5  ma.  at  a  voltage 
sufficient  for  fluoroscopic  work. 

Tuhe  Stand. — The  tube  stand  (3)  is  counterbalanced 
and  permits  placing  the  tube  in  any  desired  position.  It 
was  made  with  a  long  horizontal  extension  to  allow  work 
over  the  top  of  a  bed.  The  position  of  the  tube  during  a 
fluoroscopic  examination  should  be  controlled  by  a  prop- 
erly trained  assistant.    See  Fig.  78. 

Limitation  of  Tube  Current. — This  outfit  was  not  de- 
signed to  permit  variation  by  the  operator  of  either  cur- 
rent or  voltage.  The  power  limit  was  fixed  by  the  usual 
fuse  capacity  of  interior  wiring  for  lighting  purposes. 
More  power  would  tend  to  blow  fuses  and  thus  interfere 


180 


U.  S.  ARMY  X-RAY  MANUAL 


with  other  uses  of  these  circuits  as  well  as  delay  the  x-ray 
work.  It  gives  a  good  average  result  when  two  conditions 
are  met:  (1)  a  tube  current  of  5  ma.;  (2)  a  proper  low 
tension  voltage  applied  to  the  transformer  terminals. 

Service  Conditions. — The  user  may  find  it  necessary  to 
operate  on  any  one  of  the  following  supply  systems. 


Fig.  78.     Positions    of    parts   when    using   the   bedside    unit   with 
simple  vertical  fluoroscope  for  chest  examination  at  the  bedside. 


1.  110  volt — alternating  current. 

2.  220  volt — alternating  current. 

3.  110  volt — direct  current. 

4.  220  volt — direct  current. 

Operation. — To  operate  this  unit  the  first  thing  that  it 
is  absolutely  necessary  to  know  is  whether  alternating  or 
direct  current  is  supplied  and  at  what  voltage.    Where  any 


NEW  APPARATUS  181 

question  exists  as  to  this  point,  no  attempt  should  be  made 
to  operate  until  all  doubts  are  settled. 

This  unit  will  operate  satisfactorily  on  110  volt  alternat- 
ing current  with  no  accessories.  If  the  supply  is  110  volt 
direct  current,  a  rotary  converter  must  be  used,  Fig.  79. 
This  is  connected  by  cables  which  will  be  found  properly 
connected  to  the  switch  in  the  cabinet.     Two  leads  are  to 


Fig.  79.     Eotary  converter  used  for  direct  current  operation.   U.  S. 
Army  bedside  x-ray  unit. 

be  connected  to  the  binding  posts  on  the  rotary  marked  d.c, 
and  the  remaining  two  to  the  a.-c.  terminals  of  the  rotary. 
No  mistake  should  be  made,  as  these  cables  are  plainly 
marked.  On  220  volt,  direct  current,  this  unit  may  still 
be  used,  but  a  220  volt  rotary  will  be  required.  The  rotary 
converter  for  220  volts  is  mounted  on  a  wooden  base  and 
has  a  suitable  series  resistance.  This  rotary  is  designed 
and  adjusted  to  give  110  volts  a.c.  at  the  collector  rings 
under  load. 


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TO  OFBRaTING 
SWITCH 


TO  FOOT  ew/TCH 


T^OTnRY  CON^BRTOR 

Fig.  80.     Wiring    diagram    for    connections,    United   States   Army 
bedside  unit  for  110-220  volt,  d.c.  or  110  volt  a.c. 

182 


NEW  APPARATUS 


183 


X-Ray  Transformer. — The  x-ray  transformer  has  three 
binding  posts  numbered  1,  2,  and  3.  One  and  three  are 
used  in  all  cases  except  for  110  volt  direct-current  opera- 


rmmm 


wrn^ 


TEffNSFORMEfi 

H 


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DC-'— 


h 


Z20  VOLTS    ftC 


L 


TO  Bormy 


TO  OPEfTflTIA/G 
SWITCH 


TO  FOOT  eWITCH 


Fig.  81.     Wiring  diagram  for  connections,  United  States  Army  bed- 
side unit  for  220  volts  a.-c.  circuit. 


tion,  for  which  numbers  1  and  2  are  used.  When  the  wire 
is  removed  from  part  three  it  should  be  taped  so  as  not  to 
make  an  accidental  contact.  Fig.  80  shows  in  full  lines 
the  connection  for  110  volt  d.c,  220  d.c.  and  110  a.c.  The 
switch  must  be  closed  on  d.c.  for  both  direct-current  volt- 


184  U.  S.  ARMY  X-RAY  MANUAL 

ages,  and  on  the  a.c  side  for  both  voltages  of  alternating 
current. 

If  the  current  is  220  alternating  a  special  autotransformer 
is  required.  The  one  that  is  supplied  has  three  wires 
marked  1,  2,  and  3.  To  connect  up  for  this  voltage  (Fig. 
81)  transfer  the  line  wires  to  terminals  1  and  3  of  the  auto- 
transformer and  connect  1  of  the  x-ray  transformer  to  2 
of  the  autotransformer  and  3  of  the  x-ray  transformer  to  3 
of   autotransformer. 

Tube. — The  radiator  type  Coolidge  tube  will  be  used 
exclusively  on  these  outfits  and  little  or  no  adjustment  can 
or  will  be  left  to  the  operator.  This  tube  does  not  require 
a  rectifier  of  any  description  and  will  safely  carry  5  ma. 
for  an  indefinite  time.  For  radiographic  work  it  is  advis- 
able to  use  intensifying  screens. 

To  Adjust  the  Tube — 

1.  Remove  radiator  after  loosening  screw  at  the  end. 

2.  Carefully  place  the  two  halves  of  the  lead  glass 
shield  (4)  over  the  tube  and  fasten  together  by  means  of 
the  screws.  Do  not  turn  screws  tight  or  a  broken  shield  is 
sure  to  result. 

3.  Turn  the  tube  so  that  the  center  of  the  target  is  in 
line  with  the  opening  in  the  shield  (5). 

4.  Push  the  cork  wedges,  which  are  supplied,  in  around 
the  target  end  of  tube  first,  then  in  around  cathode  end 
so  as  to  hold  tube  firmly  in  this  position.  Replace  radia- 
tor. If  this  screw  does  not  turn  easily,  hold  the  tube  by 
the  radiator  and  not  by  the  glass.  Never  attempt  to  operate 
this  tube  without  the  radiator  in  place. 

When  placing  the  tube  in  the  holder  be  sure  that  the 
shield  containing  the  tube  is  clamped  in  the  holder  (6)  and 
not  the  tube  ends.  To  adjust  the  aluminum  filter,  which  it 
is  necessary  to  use  at  all  times,  loosen  the  two  screws  that 
hold  the  shield  together  each  side  of  the  opening,  place  the 


NEW  APPARATUS  185 

aluminum  filter  in  position  and  retighten  screws,  always  re- 
membering that  glass  will  break  if  fastened  too  tight.  The 
diaphragm  with  the  round  hole  will  cover  an  area  5  inches 
in  diameter  at  20  inches  target-screen  distance,  and  the 
square  opening  an  area  14  inches  square  at  the  same  tar- 
get-screen distance.  A  strip  of  lead  foil  may  be  attached 
by  adhesive  tape  over  the  crack  between  the  two  halves  of 
the  lead  glass  shield. 

After  everything  else  is  ready  connect  with  your  source 
of  current  and  make  sure  that  you  throw  the  two-way  switch 
to  the  correct  side.  Both  ends  are  marked  and  there  can  be 
no  excuse  for  not  doing  this  right.  After  throwing  this 
switch,  watch  the  milliammeter.  If  it  goes  to  more  than  5 
ma.,  adjust  the  resistance  wire  on  the  top  of  the  terminal 
inside  the  cabinet,  increasing  the  amount  included  between 
binding  posts ;  if  less  than  5  ma.,  reduce  the  amount  so 
included  until  the  milliammeter  reads  between  41/2  and 
5  ma. 

This  apparatus,  operated  as  directed,  will  do  the  work 
for  which  it  was  designed.  The  operator  should  not  at- 
tempt any  adjustments  other  than  those  described.  All 
others  have  been  attended  to  by  the  designers  and  makers. 
It  is  intended  that  intensifying  screens  should  be  used 
with  this  unit  for  all  radiographic  work,  unless  immobili- 
zation is  easily  accomplished. 

Care  in  Moving. — The  tube  holder  permits  of  placing 
the  tube  as  shown  in  Fig.  77,  so  that  when  moving  in  a 
ward  there  is  less  danger  of  collision  between  the  tube  and 
other  objects.  Always  move  carefully  as  the  tube  is  frag- 
ile. "When  the  holder  is  extended  the  cabinet  is  less  stable, 
and  even  more  care  must  be  taken.  When  moving  up  or 
down  stairs  always  remove  the  tube  and  clamp. 

Exposure. — The  exposure  required  with  this  outfit  will 
depend  on  conditions  as  to  film  or  plate,  and  on  whether 


186  U.  S.  ARMY  X-RAY  MANUAL 

an  intensifying  screen  is  used  and  its  speed.  If  one  is 
accustomed  to  using  40  ma.  at  about  a  5-inch  gap,  with  the 
same  conditions  as  to  distance  and  plate  or  film,  the  time 
of  exposure  is  to  be  multiplied  by  eight.  Using  an  inten- 
sifying screen  will  reduce  this  exposure  an  amount  depend- 
ing on  the  multiplying  power  of  the  screen  used.  A  good 
screen  will  reduce  the  exposure  time  to  from  1/10  to  1/15 
of  that  required  with  no  screen,  when  a  plate  or  a  single- 
coated  film  is  used. 

If  a  double-coated  film  is  supplied,  the  time  without 
screens  is  reduced  to  Yo.  For  double-coated  film  and 
single  screen,  the  time  is  further  reduced,  under  good  con- 
ditions, to  about  1/25  or  1/30  of  that  for  single  coating 
and  no  screen. 

An  excellent  chest  negative  of  a  man  of  average  size 
has  been  made  with  the  following  settings : 

Target-plate  distance — 28  inches. 

Current — 5  ma. 

Eastman  do.uble-coated  film. 

Edwards  screen  (single). 

Exposure  time — 1  sec. 

A  little  care  and  practice  will  enable  one  to  do  a  large 
amount  of  work  at  a  minimum  of  disturbance  or  discom- 
fort to  the  patient  and  Avith  quite  reasonable  exposure 
times. 

Accessory  Apparatus. — ^Hand  fiuoroscope  5x7,  the 
usual  type  for  examination  of  extremities. 

Fiuoroscope  for  chest  examination  with  special  support. 
See  Fig.  78.  This  can  be  folded  and  disassembled  for  mov- 
ing from  place  to  place. 

Reducing  goggles  are  furnished  to  enable  the  operator  to 
find  his  way  around  a  lighted  room  and  then  proceed  at 
once  to  do  reasonably  good  fluoroscopic  work.  These  con- 
tain a  red  and  a  green  celluloid  disc ;  for  a  fairly  dark 


NEW  APPARATUS  187 

room  the  red  alone  may  serve,  for  a  brightly  lighted  room 
both  are  inserted.  Just  before  bringing  the  fluoroscope 
in  position,  close  the  eyes,  raise  the  goggles  to  rest  on 
the  forehead,  and  open  the  eyes  only  after  the  fluoroscope 
is  in  position.  Reverse  these  steps  when  the  examination 
is  completed. 

Fluoroscopic  Unit. — For  the  most  successful  and  con- 
venient fluoroscopy  the  operator  should  have  control  over 
both  screen  brightness  and  the  penetration  of  the  rays.  A 
unit  embodying  these  control  features  and  of  correct  ca- 
pacity for  operation  with  the  self-rectifying  Coolidge  tube 
has  been  devised  and  is  in  limited  use  in  connection  with 
the  horizontal  and  vertical  fluoroscope,  although  not  offi- 
cially adopted  and  regularly  supplied  by  the  government. 
The  transformer  is  about  the  same  size  as  that  used  in  the 
bedside  unit  but  differs  in  having  entirely  separate  high 
tension  and  filament  transformers  in  the  same  case,  rather 
than  two  secondary  windings  energized  by  the  same  pri- 
mary as  has  the  bedside  unit.  The  primary  of  the  high  ten- 
sion transformer  and  the  primary  of  the  Coolidge  filament 
transformer  may  be  separately  controlled  by  turning  two 
knobs  on  the  control  cabinet,  giving  various  tube  currents 
and  voltages  with  a  much  simpler  adjustment  than  here- 
tofore in  use. 

This  unit  serves,  in  those  instances  where  it  is  installed, 
to  remove  the  fluoroscopic  work  from  the  large  standard 
machine  and  thereby  increase  the  capacity  of  the  x-ray 
room  without  the  addition  of  another  high  power  outfit. 
It  can  be  run  from  110  volts  a.c,  from  220  volts  a.c. 
by  means  of  a  small  autotransformer,  or  from  110  or 
220  volts  d.c.  with  a  suitable  rotary  converter.  A  wiring 
diagram  is  supplied  with  the  machine. 


STANDARD    POSITIONS 

It  has  been  the  endeavor,  in  the  following  series  of  pho- 
tographic reproductions  of  the  various  parts  of  the  body, 
to  illustrate  what  seem  the  simplest  and  most  reliable 
methods  of  securing  x-ray  plates  of  these  various  parts, 
which  are  of  most  value  in  determining  both  the  normal 
and  the  pathological  structure. 


Fig.  82.    Position:    (a)  clavicle   (b)   shoulder  joint. 


The  necessity  for  a  thorough  knowledge  of  normal  x-ray 
shadows  is  too  apparent  to  need  further  discussion  here. 
No  amount  of  study  and  observation  of  pathological  or 
abnormal  conditions  will  be  of  value  unless  the  individual 
has  first  acquired  a  true  concept  of  the  normal.    In  order 

188 


Fig.  83.     Elbow,  lateral  view. 


Fig,.  84.     Elbow,    anteroposte- 
rior view. 


^  Fig.  85.     Wrist,      anteroposte- 
rior view. 


Fig.  86.     Wrist,  lateral  view. 


190  U.  S.  ARMY  X-RAY  MANUAL 

to  obtain  such  a  concept  some  method  must  be  followed 
which  will  give  the  least  amount  of  variation  in  the  ap- 
parent size,  shape,  and  relation  of  the  parts  examined 
when  attempting  to  reproduce  the  same  results  in  the 
same  or  different  patients.     This  is  essentially  the  funda- 


FiG.  87.     Hip  joint,  anteroposterior  view. 

mental  principle  of  all  x-ray  interpretation.  It  has  been 
found  by  roentgenologists  that  this  can  only  be  accom- 
plished by  establishing  standard  relations  between  the 
source  of  the  rays,  the  sensitive  plate  and  the  part  to  be 
examined.  This  is  what  is  meant  when  speaking  of  the 
standard  positions  for  the  different  parts  of  the  body.  It 
must  be  constantly  borne  in  mind  that  even  a  slight  change 


STANDARD  POSITIONS 


191 


Fig.  88.     Knee,  antero- 
posterior view. 


Fig.  89.     Knee,  lateral  view. 


Fig.  90.     Ankle,  antero-  Fig.  91.     Ankle,  lateral  view   (mark- 

posterior  view.  er    over    internal    malleolus). 


192 


U.  S.  ARIVIY  X-RAY  MANUAL 


Fig.  93 


Fig.  92.  F  0  0  t,  anteroposterior 
view. 

Fig.  93.  Foot,  lateral  view,  mark- 
er over  first  metatarsal. 


Fig.  92 


Fig.  94.     Position  for  demonstration  of  the  posterior  portion 
of  OS  calcis;  arrow  indicates  the  direction  of  the  rays. 


STANDARD  POSITIONS  193 

in  the  relative  positions  of  the  target,  plate,  and  part 
may  result  in  some  distortion  which  might  render  the 
plate  of  doubtful  value  in  any  endeavor  to  determine  the 
abnormal  by  its  comparison  with  the  normal.  While  ex- 
perience has  shown  that  the  best  results  are  obtained  by 
adhering  to  these  positions,  it  must  be  remembered  that 
often  they  must  be  modified  to  meet  the  need  of  individual 
cases. 

Several  illustrations  of  standard  positions  which  are 
not  shown  elsewhere  in  the  manual  are  here  grouped  to- 
gether. 

These  are  the  only  parts  of  the  body  which  the  x-ray 
manipulator  should  be  allowed  to  examine.  All  other  ex- 
aminations require  the  personal  attention  of  the  roent- 
genologist. 


DANGERS   AND    PROTECTION 

Dangers  from  the  X-Rays.— The  danger  to  the  skin  of 
operator  and  patient  requires  careful  consideration  in 
order  to  avoid  serious  injury.  It  is  customary  to  speak  of 
a  dose  that  will  cause  a  slight  temporary  redness  of  the 
skin  as  an  erythema  dose.  This  dose  undoubtedly  varies 
considerably  according  to  the  age  of  the  patient  and  to 
the  judgment  of  the  observer  as  to  the  extent  of  redness 
which  may  be  called  "slight." 

The  skin  dose  will  depend  on  the  following  factors : 

1.  Target-skin  distance. 

2.  Spark  gap  (voltage). 

3.  Current  through  the  tube. 

4.  Time  or  duration  of  exposure. 

5.  Nature  and  thickness  of  filter  used. 

While  complete  agreement  as  to  what  will  give  an  ery- 
thema dose  can  hardly  be  expected,  all  will  agree  that  the 
dose  will  increase  with  the  duration  of  exposure,  with  the 
current  and  with  the  spark  gap ;  and  will  decrease  as  dis- 
tance between  target  and  skin  is  increased  and  as  thicker 
filters  are  used. 

It  is  convenient  in  this  connection  to  combine  the  tube 
current  in  ma.  and  the  time  in  minutes,  and  speak  of 
milliampere  minutes,  but  it  must  de  clearly  understood 
that  the  number  of  milliampere  minutes  allowable  varies 
with  the  spark  gap. 

Working  at  a  target-skin  distance  of  20  inches  and  a 
5-inch  gap,  45  milliampere  minutes  may  be  safely  allowed 

194 


DANGERS  AND  PROTECTION  195 

if  no  filter  is  used.  For  general  safety,  a  filter  of  1  mm. 
of  aluminum  is  advised,  and  then  an  increase  of  about  40 
per  cent  may  be  allowed — or  about  60  ma.  minutes  may 
be  taken  as  a  safe  total  to  be  received  by  the  skin  at 
this  gap  and  target-skin  distance.  Thus,  at  5  ma. — 5-inch 
gap — 20  inches — 1  mm.  al.,  a  total  of  twelve  minutes  may 
be  used  on  one  skin  area  for  fluoroscopic  examination,  if 
no  radiograph  is  to  he  taken. 

If  20  ma.  minutes  at  a  5-inch  gap  were  used  in  fluoro- 
scopy there  remains  only  40  ma.  minutes  for  radiographic 
work.  If  40  ma.  is  used  and  10  seconds  is  required  for  a 
negative,  only  6  plates  could  be  safely  made.  On  this 
account  it  is  wise  to  make  fluoroscopic  examinations  as 
brief  as  is  consistent  with  good  work  and  to  use  intensify- 
ing screens  in  serial  radiography. 

A  very  important  point  to  remember  is  that  when  using 
a  smaller  gap,  although  the  amount  of  radiation  reaching 
the  skin  is  less  for  the  same  current,  the  exposure  required 
in  radiographic  work  is  very  much  longer.  To  get  the 
same  plate  density  at  lower  gaps,  the  skin  risk  is  greater. 
Many  cases  of  dermatitis  are  due  to  prolonged  or  re- 
peated exposure  with  too  small  a  back-up  gap  for  the  work 
in  hand. 

Be  sure  that  unfiltered  rays  along  the  axis  of  the  tube, 
which  do  not  have  to  pass  through  the  lead  glass  bowl,  do 
not  reach  the  patient. 

When  an  erythema  dose  is  reached  or  approached,  an 
interval  of  three  weeks  should  elapse  before  again  expos- 
ing. 

Exposure  beyond  an  erythema  dose  may  be  justified 
when  circumstances  arise  of  an  unusual  nature.  But  the 
surgeon  or  attending  physician  should  be  warned  by  the 
roentgenologist  before  such  a  risk  is  to  be  taken. 

Protection  of  the  Operator  from  the  X-Rays. — The  ele- 


196  U.  S.  ARMY  X-RAY  MANUAL 

ment  of  increase  in  the  work  time  makes  care  in  the  protec- 
tion of  the  operator  of  extreme  importance.  Two  things 
are  clear  in  this  matter :  First,  that  effects  are  cumulative ; 
second,  that  evidence  of  injury  may  develop  late.  Since  the 
demands  of  the  art  fix  the  amount  of  radiation  for  specific 
purposes,  the  operator  can  do  only  three  things  for  self- 
protection. 

1.  Increase  the  distance  from  the  target  to  any  part 
of  his  body. 

2.  Interpose  absorbing  material  between  himself  and 
the  tube. 

3.  Reduce  the  time  devoted  to  the  work. 

The  first  of  these  is  applicable  in  radiographic  work 
only,  as  in  fluoroscopy  he  must  work  at  close  range.  The 
third  can  have  only  limited  application  in  a  military  hos- 
pital during  war,  so  the  second  is  the  practical  method. 

The  followin'g  suggestions  are  offered  in  the  hope  that 
they  may  be  applied : 

1.  That  in  all  radiographic  and  treatment  work  no 
direct  rays  be  allowed  to  reach  the  operator's  body  without 
passing  through  at  least  1/16  inch  of  lead  where  lead  can 
be  used.  Lead  glass  should  have  an  absorption  equivalent 
to  1/32  inch  of  lead. 

2.  That  in  addition  to  this  lead  protection,  the  opera- 
tor keep  several  feet  from  the  tube  in  treatment  and  heavy 
radiography. 

3.  That  in  using  either  a  vertical  or  a  horizontal  flu- 
oroscope,  a  careful  test  be  made  to  ensure  that  no  direct 
rays  come  through  bad  joints,  holes  in  lead,  or  other  un- 
protected openings. 

4.  That  the  fluoroscopic  screen  be  protected  with  lead 
glass  at  least  equivalent  to  1/32  inch  of  lead. 

5.  That  the  lead  glass  and  sheet  lead  on  the  frame  over- 
lap at  least  %  inch. 


DANGERS  AND  PROTECTION  197 

6.  That  the  diaphragm  never  be  opened  or  moved  so 
as  to  send  part  of  the  beam  past  the  screen,  and  1  mm.  of 
aluminum  be  used  as  a  filter  in  all  cases. 

7.  That  in  horizontal  fluoroscopy  some  protection  be 
given  for  rays  scattered  at  right  angles  to  the  patient's 
body. 

8.  That  the  operator  study  his  working  conditions  so 
as  to  secure  the  results  required  in  the  minimum  time. 

Tinder  no  circumstances  should  an  operator  use  any  part 
of  his  body  for  fluoroscopic  demonstration,  nor  should  he 
hold  any  plate  or  dental  film  in  position  during  exposure. 

It  should  be  understood  that  the  final  responsibility  for 
protection,  both  of  the  patient  and  the  operator,  rests  on 
the  roentgenologist  himself,  and  after  his  apparatus  is 
installed  he  should  not  neglect  to  test  for  gross  leaks  and 
insufficient  protection. 

The  fluoroscopic  screen  in  a  well-darkened  room  will 
help  to  find  where  danger  may  lurk  but  gives  no  idea  of 
the  amount  of  radiation  involved  in  the  indicated  direc- 
tions. 

According  to  the  work  of  Pfahler  and  others,  on  a  5-inch 
gap  the  number  of  milliampere-minutes  required  with  un- 
fixltered  radiation  for  a  full  erythema  dose  at  20  inches, 
allowing  no  factor  of  safety,  will  be  about  60.  This  means 
that  without  filter,  5  ma.,  at  a  5-inch  gap,  20  inches  tar- 
get-skin distance,  12  minutes  will  almost  certainly  give 
a  skin  inflammation. 

A  test  of  the  danger  may  be  made  as  follows :  take  a  few 
dental  films,  number  them,  and  place  in  the  position  occu- 
pied by  the  operator's  body  when  at  work,  but  attached 
to  his  clothing.  After  he  has  worked  for  some  time,  de- 
velop these  films  and  note  their  general  density. 

Then  using  the  above  data,  5  ma.  at  20-inch  target-plate 
distance  and  a  5-inch  gap,  expose  a  series  of  films  for  defi- 


198  U.  S.  ARMY  X-RAY  MANUAL 

nite  fractions  of  the  time  required  for  an  erythema  dose. 
These  fractions  must  be  small  and  care  must  be  taken  to 
develop  these  films  exactly  as  the  test  films  were  devel- 
oped. In  this  way  it  is  possible  to  determine  the  time  the 
operator  must  work  to  approximate  an  erythema  dose. 
Probably  %  such  a  dose  per  month  would  not  have  any 
serious  effect. 

Electrical  Dangers. — In  the  use  of  high-power  x-ray  ap- 
paratus, care  must  be  taken  to  avoid  discharge  from  high 
tension  lines  to  earth  through  the  body  of  either  patient 
or  operator.  Fatal  results  may  follow,  and  in  any  event 
the  nervous  shock  to  the  patient  may  be  serious.  Danger 
arises  from  sparks  followed  by  an  arc  discharge  from  the 
high  voltage  line  to  the  body,  thence  to  earth. 

To  get  such  a  discharge,  we  must  have : 

1.  Grounding  of  patient  or  contact  with  badly  insu- 
lated grounding  material. 

2.  So  short  an  air  distance  from  some  part  of  the  high 
tension  system  as  will  allow  a  break  over  spark. 

A  single  spark,  while  disconcerting,  is  not  dangerous 
to  life,  but  it  serves  to  pave  the  way  for  a  heavy  discharge 
"from  the  line  if  the  supply  is  maintained.  On  static  ma- 
chines and  most  induction  coils,  body  connection  so  re- 
duces the  line  voltage  as  to  preclude  any  fatal  amount  of 
current ;  but  with  the  modern  high  power  transformer  it  is 
a  different  matter. 

The  danger  of  an  initial  spark-over  to  the  body  is 
solely  a  matter  of  line  to  skin  distance  and  voltage  from 
line  to  earth.  When  a  tube  is  taking  current,  the  voltage 
from  either  line  to  earth  is  less  than  it  would  be  on  the 
same  control  setting  if  no  current  were  passing.  Hence, 
failure  of  the  tube  to  take  current  at  any  time  tends  to 
cause  discharge  to  the  patient.  The  following  are  the  com- 
mon ways  in  which  this  may  happen : 


DANGERS  AND  PROTECTION  199 

1.  Failure  to  complete  high  tension  connection. 

2.  "Cranky"  gas-tube. 

3.  Failure  to  light  Coolidge  filament  before  turning  on 
high  tension. 

4.  Break  or  disconnection  of  Coolidge  filament  circuit 
while  running. 

5.  Attempting  to  pass  current  through  Coolidge  tube 
in  wrong  direction. 

Another  cause  for  spark-over  is  the  high  tension  surge 
often  caused  on  closing  the  primary  switch  of  the  trans- 
former. 

Keep  all  high  tension  lines  at  least  twice  as  far  from 
any  portion  of  the  patient  as  the  working  spark  gap. 
Thus,  if  using  an  equivalent  gap  of  6  inches,  allow  no 
wire  closer  than  12  inches.  A  grounded  metal  or  con- 
ducting screen  between  the  high  tension  lines  and  the  pa- 
tient is  complete  protection  for  the  patient;  thus,  a  hori- 
zontal fluoroscope  with  a  grounded  frame  is  safe  with 
the  tube  below;  but  when  the  patient  is  between  the  high 
tension  line  and  a  grounded  metal  or  conducting  table, 
danger  is  greatly  increased. 

Type  of  Control. — Much  has  been  said  of  the  relative 
danger  with  various  controls.  Simply  stated  it  amounts 
to  this:  the  rise  in  voltage  when  the  tube  fails  to  take 
current  is  very  much  greater  on  a  resistance  control  (See 
Figs.  19  and  20),  so  that  the  chance  of  an  initial  spark 
is  greater;  but  after  such  a  spark,  the  chance  of  a  fol- 
lowing arc  is  reduced  by  reason  of  resistance  in  the  pri- 
mary circuit. 

With  autotransformer  control,  or  operation  without  re- 
sistance— i.  e.,  with  rheostat  all  out — the  rise  in  voltage 
on  open  circuit  is  less;  but  if  an  arc  is  started,  it  is  very 
dangerous.  A  quick-acting,  over-load  primary  break  is 
very  desirable. 


200  U.  S.  ARMY  X-RAY  MANUAL 

Resuscitation  from  Electric  Shock  or  Asphyxiation. — 

The  prone  pressure  method  of  artificial  respiration,  de- 
vised by  Prof.  Schaefer,  of  Edinburgh,  has  been  advocated 
as  the  most  effective  method  by  the  United  States  Bureau 
of  Mines'  Committee.  This  method  can  be  used  with 
oxygen  inhalator.  It  should  always  be  used  immediately 
to  resuscitate  asphyxiated  persons  and  kept  up  continu- 
ously until  approved  mechanical  resuscitating  devices  are 


Fig.   95.     Eesuscitation  from  electric  shock. 
Above — Expiration,   pressure    on.     Below — Inspiration,   pressure   off. 

brought  to  the  scene  and  adjusted  on  the  patient.  Heart 
stimulant  should  be  given  as  frequently  as  necessary. 

This  system  can  be  used  in  cases  of  electric  shock,  after 
the  victim  has  been  removed  from  the  live  conductor,  in 
cases  of  gas  poisoning  or  asphyxiation  from  any  cause. 
Artificial  respiration  should  he  begun  promptly,  as  life 
persists  only  a  few  minutes  after  breathing  stops. 

Quickly  feel  with  your  finger  in  the  victim's  mouth 
and  throat  and  remove  any  foreign  body  (tobacco,  false 
teeth,  etc.),  then  begin  artificial  respiration  at  once.  Do 
not  stop  to  loosen  patient's  clothing;  every  moment  is 
precious. 


DANGERS  AND  PROTECTION  201 

Lay  the  subject  on  his  belly,  with  arms  extended  as 
straight  forward  as  possible,  and  with  face  to  one  side, 
so  that  the  nose  and  mouth  are  free  for  breathing.  Draw 
forward  the  subject's  tongue. 

Do  not  permit  bystanders  to  crowd  around  and  shut 
off  the  air. 

Kneel,  straddling  the  subject's  thighs  and  facing  his 
head;  rest  the  palms  of  your  hands  on  the  loins  with 
thumbs  nearly  touching  and  with  fingers  spread  over  the 
lower  ribs.    Fig.  95. 

With  arms  held  straight,  swing  forward  slowly,  so  that 
the  weight  of  your  body  is  gradually  brought  to  bear 
upon  the  subject.  This  operation,  which  should  take  two 
or  three  seconds,  must  not  be  violent,  lest  internal  organs 
be  injured.    The  air  is  thus  forced  out  of  the  lungs. 

Now  immediately  swing  backward  so  as  to  remove  the 
pressure,  but  leave  your  hands  in  place.  The  air  thus^ 
enters  the  lungs. 

After  two  seconds  swing  forward  again,  repeating  this 
operation  twelve  to  fifteen  times  to  a  minute,  a  complete 
respiration  every  four  or  five  seconds.  AVhile  this  is  be- 
ing done,  an  assistant  should  loosen  any  tight  clothing 
about  subject's  neck,  chest  or  waist. 

Continue  artificial  respiration  (if  necessary)  two  hours 
or  longer,  without  interruption,  until  natural  breathing 
is  restored.  Even  when  natural  breathing  begins,  care- 
fully watch  that  it  continues.  If  it  stops,  begin  artificial 
respiration  again. 

Keep  subject  w^arm  by  applying  a  proper  covering  or 
artificial  heat,  hot  water  bags,  etc. 

Do  not  give  stimulants  or  liquids  by  mouth  until  sub- 
ject is  fully  conscious. 


^     THE      \ 

Strive  for  Imaging  Excellence 

MIotto  t>f  the  United  States  Army  X-Ray  Specialist  Course 

■»  - 

HEALTH 
SCIENCES 
LIBRARY 


Between  January,  1984  and  January,  1987,  I  was  fortunate  to 
serve  in  the  United  States  Army  in  the  capacity  of  Chief  of  the 
X-Ray  Branch  and  Program  Director  for  the  United  States  Army 
X-Ray  Specialist  Course  at  the  Academy  of  the  Health  Sciences, 
Fort  Sam  Houston,  Texas.  As  a  Medical  Service  Corps  officer  with 
the  rank  of  Captain,  I  was  faced  with  the  sobering  responsibility 
of  leading  approximately  30  x-ray  instructors  in  the  largest  medical 
radiography  training  mission  in  the  free  world.  One  of  my  major 
goals  was  to  analyze  the  existing  curriculum  and  generate  valid 
recommendations  for  educational  improvements  to  my  military 
superiors. 

After  developing  goals  and  hypotheses  concerning  the  curricular 
variables  in  question  and  after  defming  assumptions,  limitations, 
and  research  methods,  I  conducted  a  review  of  the  available 
research  and  literature  on  the  subject  of  radiography  education  in 
the  United  States  Army.  Aside  from  the  X-Ray  Branch  documents, 
that  went  back  about  10  years,  there  was  virtually  no  readily 
available  information  about  the  origin  of  the  Army  radiography 
educational  mission  or  its  clinical  mission. 

Continuing  the  search,  I  learned  of  the  first  use  of  x-rays  by  the 
Army  during  the  Spanish  American  War  of  1 898  and  that  the  begin- 
ning of  America's  involvement  in  World  War  I  during  1917  marked 
the  first  formalization  of  radiography  training  in  the  Army  on  a 
tremendously  large  scale.  Within  approximately  one  year,  the 
United  States  Army  medical  department  set  up  three  training  centers 
at  the  U.S.  Army  Medical  School  in  Washington,  D.C.,  Fort  Riley, 


Kansas,  and  Camp  Greenleaf,  Georgia.  After  the  close  of  the  Fort 
Riley  school,  the  majority  of  Army  X-Ray  Manipulators,  as  they 
were  called,  were  trained  at  Camp  Greenleaf.  For  each  officer— 
roentgenologist  (physician)  trained,  there  were  two  x-ray 
manipulators.  At  one  time.  Camp  Greenleaf  had  plans  to  generate 
120  military  roentgenologists.  Considering  that  the  U.S.  Army 
Medical  School  at  one  time  generated  150  x-ray  manipulators  per 
month,  one  may  safely  conclude  that  several  thousand  U.S.  Army 
x-ray  manipulators  must  have  been  trained  for  duty  during  World 
War  I. 

Developing  significant  interest  in  WWI  Army  Radiography,  I 
searched  extensively  for  the  infamous  textbook  developed  during 
this  period  for  training  the  Army  x-ray  manipulator  towards  the 
close  of  the  war.  It's  tide  was.  The  United  States  Army  X-Ray 
Manual.  If  I  could  get  my  hands  on  this  textbook.  I  knew  I  would 
have  a  glimpse  into  the  past  that  few  have  ever  attained  in 
radiography  education  .  As  my  library  search  went  out,  I  happened 
to  locate  one.  However,  I  was  only  able  to  keep  it  for  a  cou- 
ple of  days  absorbing  as  much  as  I  could.  Upon  returning  it  to 
the  library,  I  thought  that  some  old  bookstore  would  surely  know 
where  I  could  find  a  copy  of  the  Manual  for  my  personal  library. 
Searching  and  calling  on  old  bookstores  that  catered  to  the  antique 
book  market,  I  was  unable  to  locate  the  Manual.  However,  I  did 
follow  up  on  one  of  the  greatest  tips  in  my  life. 

Calling  this  one  bookstore,  the  owner  said  that  I  should  try  to 
find  a  person  named  George  Miller  who  was  supposedly  trained 
as  an  Army  radiographer.  Searching  the  telephone  directory,  I  came 
upon  his  name  and  address.  I  called  Mr.  Miller  that  same  day, 
the  Fourth  of  July,  1985.  George  told  me  to  come  over,  and  that 
he  had  the  book.  When  I  got  there,  I  was  completely  dumbfounded 
when  he  not  only  enlightened  me  on  his  extraordinary  military 
career  spanning  some  30  years,  but  when  he  handed  me  two  books 
and  said,  "Here,  I  won't  be  needing  these.  You  can  have  them." 
The  two  books  were.  The  United  States  Army  X-Ray  Manual  and 
the  Extract  from  the  United  States  Army  X-Ray  Manual. 

Mr.  Miller  explained  to  me  that  when  he  trained  as  an  Army 
radiographer  in  1932,  the  Extract  was  given  to  the  enlisted  per- 
sonnel who  were  training  to  be  x-ray  technicians  and  the  Manual 


was  given  to  the  doctors  who  were  training  to  become  mihary  roent- 
genologists. I  never  expected  to  receive  such  a  gift  from  Mr.  Miller. 
Through  meeting  him,  I  have  been  extremely  blessed  with  some 
incredible  knowledge  concerning  the  role  of  the  radiographer  in 
the  United  States  Army.  And,  George  and  I  have  become  genuine 
friends.  Mr.  Miller  retired  at  the  rank  of  Master  Sergeant  in  the 
early  1950s.  At  one  time  he  served  as  the  Non-commissioned  Of- 
ficer in  Charge  of  the  X-Ray  Branch  when  all  of  the  formal 
radiography  training  centered  at  Fort  Sam  Houston,  Texas  im- 
mediately after  World  War  II. 

After  completing  the  assessment  on  the  Army  radiography  cur- 
riculum and  taking  stock  of  a  training  process  that  spans  this  en- 
tire century,  I  realized  that  the  Extract  that  Mr.  Miller  gave  me 
was  one  of  the  first,  if  not  the  first,  educational  textbook  produced 
for  the  training  of  radiographers  in  North  America.  Later,  I  would 
learn  that  Chapter  1,  entitled  "X-Ray  Physics"  was  written  by 
Lieutenant  Colonel  John  Sanford  Shearer,  Ph.D.  This  physicist 
taught  at  Cornell  University  and  published  extensively  between 
1897  and  1922  on  the  various  aspects  of  the  physical  foundations 
of  radiography.  His  insight  and  tremendous  intensity  of  concern 
for  the  training  of  American  radiographers  and  roentgenologists 
was  ten  years  before  Ed  C.  Jerman's  contributions  to  the  field. 

The  Extract  that  you  now  hold  is  a  real  treasure  for  those  who 
have  a  sense  of  history  about  radiography.  Show  it  to  your  col- 
leagues and  marvel  at  the  x-ray  technology  of  World  War  I  and 
how,  even  though  things  look  outdated,  many  things  have  not  really 
changed.  Show  it  to  the  new  students  in  medical  imaging  and  let 
them  begin  to  sense  an  appreciation  of  the  present  medical  imag- 
ing technology.  Remember,  also,  that  although  the  origination  of 
this  historical  document  began  with  those  scientists  and  physician- 
roentgenologists  of  the  WWI  period  whose  roentgenology  re- 
quirements gave  birth  to  the  Army  x-ray  manipulators,  it  was 
Master  Sergeant  (Retired)  George  Miller,  who  kept  this  rare  edi- 
tion all  these  years  so  that  we  all  could  enjoy  a  tremendous 
radiography  flashback. 

Thanks  George,  on  behalf  of  all  American  radiographers. 

Finally,  if  you  are  seeking  to  know  much  more  about  the  Army 
radiography  evolution  between  1917  and  1946,  please  consult  three 


articles  that  were  published  in  Radiologic  Technology  in  1985, 
1986,  and  1987.  If  you  would  like  to  know  the  results  of  the  assess- 
ment of  the  Army  radiography  curriculum  that  I  conducted  between 
1984  and  1987,  write  to  The  Bumell  Company /Publishers,  Inc.,  for 
a  copy  of  my  findings.  If  you  would  like  first-hand  knowledge  and 
experience  about  what  it  is  like  being  a  genuine  Army  radiographer, 
I  know  an  educational  program  with  a  long  and  proud  tradition 
of  training.  In  today's  Army  you  can  be  all  that  you  can  be  and 
then  some.  You  can  learn  how  to  "Strive  for  Imaging  Excellence" 
at  the  Army  radiography  program,  Fort  Sam  Houston,  Texas. 


O.  Gary  Lauer,  Ph.D.,  RT  (R)  ARRT 


This  Edition  published  1987  by 

The  Burnell  Co./Publishers,  Inc. 

P.O.  Box  304 
Mankato,  MN  56002 


COLUMBIA  UNIVERSITY  LIBRARIES  (hsi.stx) 

RC  78.5  .U55  1918  C.1 

Extract  from  the  United  States  Army  X-ra 


2002255545 


